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 $48.43   10.705%   $53.6144   $53.61   $53.60   $53.60  
  Purchase #2 $154.97   11.701%   $173.103   $173.10   $173.10   $173.10  
  Purchase #3 $24.95   7.334%   $26.7798   $26.78   $26.80   $26.80  
  Purchase #4 $31.54   13.246%   $35.7178   $35.72   $35.70   $35.70  
  Purchase #5 $197.63   5.739%   $208.972   $208.97   $208.95   $209.00  
  Purchase #6 $171.38   6.320%   $182.2112   $182.21   $182.20   $182.20  
  Purchase #7 $182.47   11.188%   $202.8847   $202.88   $202.90   $202.90  
  7 purchase totals = $811.37       $883.2829   $883.27   $883.25   $883.30