Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $123.60   4.345%   $128.9704   $128.97   $128.95   $129.00  
  Purchase #2 $129.48   12.627%   $145.8294   $145.83   $145.85   $145.80  
  Purchase #3 $231.38   12.179%   $259.5598   $259.56   $259.55   $259.60  
  Purchase #4 $146.50   12.621%   $164.9898   $164.99   $165.00   $165.00  
  Purchase #5 $117.46   12.823%   $132.5219   $132.52   $132.50   $132.50  
  Purchase #6 $249.32   13.717%   $283.5192   $283.52   $283.50   $283.50  
  Purchase #7 $116.84   3.377%   $120.7857   $120.79   $120.80   $120.80  
  7 purchase totals = $1,114.58       $1,236.1762   $1,236.18   $1,236.15   $1,236.20