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 $89.51   7.565%   $96.2814   $96.28   $96.30   $96.30  
  Purchase #2 $94.38   11.713%   $105.4347   $105.43   $105.45   $105.40  
  Purchase #3 $85.32   10.168%   $93.9953   $94.00   $94.00   $94.00  
  Purchase #4 $51.57   7.856%   $55.6213   $55.62   $55.60   $55.60  
  Purchase #5 $22.98   11.642%   $25.6553   $25.66   $25.65   $25.70  
  Purchase #6 $88.78   9.263%   $97.0037   $97.00   $97.00   $97.00  
  Purchase #7 $111.70   7.255%   $119.8038   $119.80   $119.80   $119.80  
  7 purchase totals = $544.24       $593.7955   $593.79   $593.80   $593.80