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 $241.51   5.413%   $254.5829   $254.58   $254.60   $254.60  
  Purchase #2 $44.96   6.868%   $48.0479   $48.05   $48.05   $48.00  
  Purchase #3 $55.34   9.412%   $60.5486   $60.55   $60.55   $60.50  
  Purchase #4 $126.78   9.425%   $138.729   $138.73   $138.75   $138.70  
  Purchase #5 $76.71   3.573%   $79.4508   $79.45   $79.45   $79.50  
  Purchase #6 $35.57   11.387%   $39.6204   $39.62   $39.60   $39.60  
  Purchase #7 $169.76   10.558%   $187.6833   $187.68   $187.70   $187.70  
  7 purchase totals = $750.63       $808.6629   $808.66   $808.70   $808.60