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 $48.53   9.834%   $53.3024   $53.30   $53.30   $53.30  
  Purchase #2 $88.52   7.559%   $95.2112   $95.21   $95.20   $95.20  
  Purchase #3 $211.45   4.334%   $220.6142   $220.61   $220.60   $220.60  
  Purchase #4 $81.57   12.620%   $91.8641   $91.86   $91.85   $91.90  
  Purchase #5 $222.28   5.229%   $233.903   $233.90   $233.90   $233.90  
  Purchase #6 $26.69   13.803%   $30.374   $30.37   $30.35   $30.40  
  Purchase #7 $65.42   5.119%   $68.7688   $68.77   $68.75   $68.80  
  7 purchase totals = $744.46       $794.0377   $794.02   $793.95   $794.10