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 $61.53   11.200%   $68.4214   $68.42   $68.40   $68.40  
  Purchase #2 $172.48   6.238%   $183.2393   $183.24   $183.25   $183.20  
  Purchase #3 $59.46   4.411%   $62.0828   $62.08   $62.10   $62.10  
  Purchase #4 $84.59   11.638%   $94.4346   $94.43   $94.45   $94.40  
  Purchase #5 $69.56   4.446%   $72.6526   $72.65   $72.65   $72.70  
  Purchase #6 $44.92   13.351%   $50.9173   $50.92   $50.90   $50.90  
  Purchase #7 $244.51   6.809%   $261.1587   $261.16   $261.15   $261.20  
  7 purchase totals = $737.05       $792.9067   $792.90   $792.90   $792.90