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 $84.75   12.265%   $95.1446   $95.14   $95.15   $95.10  
  Purchase #2 $112.84   6.597%   $120.2841   $120.28   $120.30   $120.30  
  Purchase #3 $155.27   12.523%   $174.7145   $174.71   $174.70   $174.70  
  Purchase #4 $25.63   6.459%   $27.2854   $27.29   $27.30   $27.30  
  Purchase #5 $127.27   6.460%   $135.4916   $135.49   $135.50   $135.50  
  Purchase #6 $178.92   13.363%   $202.8291   $202.83   $202.85   $202.80  
  Purchase #7 $26.93   4.619%   $28.1739   $28.17   $28.15   $28.20  
  7 purchase totals = $711.61       $783.9232   $783.91   $783.95   $783.90