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 $13.86   6.555%   $14.7685   $14.77   $14.75   $14.80  
  Purchase #2 $156.52   9.398%   $171.2297   $171.23   $171.25   $171.20  
  Purchase #3 $65.84   4.228%   $68.6237   $68.62   $68.60   $68.60  
  Purchase #4 $237.82   7.761%   $256.2772   $256.28   $256.30   $256.30  
  Purchase #5 $242.58   8.390%   $262.9325   $262.93   $262.95   $262.90  
  Purchase #6 $210.52   7.644%   $226.6121   $226.61   $226.60   $226.60  
  Purchase #7 $213.67   9.785%   $234.5776   $234.58   $234.60   $234.60  
  7 purchase totals = $1,140.81       $1,235.0213   $1,235.02   $1,235.05   $1,235.00