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 $82.96   6.699%   $88.5175   $88.52   $88.50   $88.50  
  Purchase #2 $114.74   3.406%   $118.648   $118.65   $118.65   $118.60  
  Purchase #3 $247.83   10.420%   $273.6539   $273.65   $273.65   $273.70  
  Purchase #4 $173.28   12.692%   $195.2727   $195.27   $195.25   $195.30  
  Purchase #5 $70.98   11.562%   $79.1867   $79.19   $79.20   $79.20  
  Purchase #6 $200.48   4.416%   $209.3332   $209.33   $209.35   $209.30  
  Purchase #7 $249.34   12.494%   $280.4925   $280.49   $280.50   $280.50  
  7 purchase totals = $1,139.61       $1,245.1045   $1,245.10   $1,245.10   $1,245.10