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 $167.60   9.193%   $183.0075   $183.01   $183.00   $183.00  
  Purchase #2 $94.84   8.259%   $102.6728   $102.67   $102.65   $102.70  
  Purchase #3 $104.49   11.748%   $116.7655   $116.77   $116.75   $116.80  
  Purchase #4 $119.38   4.620%   $124.8954   $124.90   $124.90   $124.90  
  Purchase #5 $117.65   3.758%   $122.0713   $122.07   $122.05   $122.10  
  Purchase #6 $207.85   12.573%   $233.983   $233.98   $234.00   $234.00  
  Purchase #7 $120.83   12.496%   $135.9289   $135.93   $135.95   $135.90  
  7 purchase totals = $932.64       $1,019.3244   $1,019.33   $1,019.30   $1,019.40