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 $51.65   13.647%   $58.6987   $58.70   $58.70   $58.70  
  Purchase #2 $100.40   12.344%   $112.7934   $112.79   $112.80   $112.80  
  Purchase #3 $24.33   8.421%   $26.3788   $26.38   $26.40   $26.40  
  Purchase #4 $177.79   11.252%   $197.7949   $197.79   $197.80   $197.80  
  Purchase #5 $131.69   8.197%   $142.4846   $142.48   $142.50   $142.50  
  Purchase #6 $193.28   10.399%   $213.3792   $213.38   $213.40   $213.40  
  Purchase #7 $200.87   7.584%   $216.104   $216.10   $216.10   $216.10  
  7 purchase totals = $880.01       $967.6336   $967.62   $967.70   $967.70