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 $68.46   7.327%   $73.4761   $73.48   $73.50   $73.50  
  Purchase #2 $75.56   8.192%   $81.7499   $81.75   $81.75   $81.70  
  Purchase #3 $153.38   11.685%   $171.3025   $171.30   $171.30   $171.30  
  Purchase #4 $182.54   7.249%   $195.7723   $195.77   $195.75   $195.80  
  Purchase #5 $71.45   5.849%   $75.6291   $75.63   $75.65   $75.60  
  Purchase #6 $146.50   4.477%   $153.0588   $153.06   $153.05   $153.10  
  Purchase #7 $110.75   12.433%   $124.5195   $124.52   $124.50   $124.50  
  7 purchase totals = $808.64       $875.5082   $875.51   $875.50   $875.50