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 $60.66   8.131%   $65.5923   $65.59   $65.60   $65.60  
  Purchase #2 $250.95   4.756%   $262.8852   $262.89   $262.90   $262.90  
  Purchase #3 $240.64   9.325%   $263.0797   $263.08   $263.10   $263.10  
  Purchase #4 $236.45   13.237%   $267.7489   $267.75   $267.75   $267.70  
  Purchase #5 $138.75   5.635%   $146.5686   $146.57   $146.55   $146.60  
  Purchase #6 $50.72   10.318%   $55.9533   $55.95   $55.95   $56.00  
  Purchase #7 $53.98   11.782%   $60.3399   $60.34   $60.35   $60.30  
  7 purchase totals = $1,032.15       $1,122.1679   $1,122.17   $1,122.20   $1,122.20