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 $55.47   13.604%   $63.0161   $63.02   $63.00   $63.00  
  Purchase #2 $58.47   6.726%   $62.4027   $62.40   $62.40   $62.40  
  Purchase #3 $219.91   9.741%   $241.3314   $241.33   $241.35   $241.30  
  Purchase #4 $88.68   9.521%   $97.1232   $97.12   $97.10   $97.10  
  Purchase #5 $112.71   4.155%   $117.3931   $117.39   $117.40   $117.40  
  Purchase #6 $194.94   8.316%   $211.1512   $211.15   $211.15   $211.20  
  Purchase #7 $213.98   12.658%   $241.0656   $241.07   $241.05   $241.10  
  7 purchase totals = $944.16       $1,033.4833   $1,033.48   $1,033.45   $1,033.50