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 $85.98   11.873%   $96.1884   $96.19   $96.20   $96.20  
  Purchase #2 $108.85   12.823%   $122.8078   $122.81   $122.80   $122.80  
  Purchase #3 $230.88   7.266%   $247.6557   $247.66   $247.65   $247.70  
  Purchase #4 $233.98   8.303%   $253.4074   $253.41   $253.40   $253.40  
  Purchase #5 $59.46   12.212%   $66.7213   $66.72   $66.70   $66.70  
  Purchase #6 $43.63   4.802%   $45.7251   $45.73   $45.75   $45.70  
  Purchase #7 $120.40   12.789%   $135.798   $135.80   $135.80   $135.80  
  7 purchase totals = $883.18       $968.3037   $968.32   $968.30   $968.30