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 $247.68   10.131%   $272.7725   $272.77   $272.75   $272.80  
  Purchase #2 $227.61   13.521%   $258.3851   $258.39   $258.40   $258.40  
  Purchase #3 $103.70   6.676%   $110.623   $110.62   $110.60   $110.60  
  Purchase #4 $171.67   10.322%   $189.3898   $189.39   $189.40   $189.40  
  Purchase #5 $22.52   13.769%   $25.6208   $25.62   $25.60   $25.60  
  Purchase #6 $55.87   4.715%   $58.5043   $58.50   $58.50   $58.50  
  Purchase #7 $125.97   9.837%   $138.3617   $138.36   $138.35   $138.40  
  7 purchase totals = $955.02       $1,053.6572   $1,053.65   $1,053.60   $1,053.70