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 $207.51   13.506%   $235.5363   $235.54   $235.55   $235.50  
  Purchase #2 $232.71   3.775%   $241.4948   $241.49   $241.50   $241.50  
  Purchase #3 $97.61   7.546%   $104.9757   $104.98   $105.00   $105.00  
  Purchase #4 $239.46   6.355%   $254.6777   $254.68   $254.70   $254.70  
  Purchase #5 $244.40   5.870%   $258.7463   $258.75   $258.75   $258.70  
  Purchase #6 $115.96   8.417%   $125.7204   $125.72   $125.70   $125.70  
  Purchase #7 $22.78   10.533%   $25.1794   $25.18   $25.20   $25.20  
  7 purchase totals = $1,160.43       $1,246.3306   $1,246.34   $1,246.40   $1,246.30