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 $67.46   11.719%   $75.3656   $75.37   $75.35   $75.40  
  Purchase #2 $230.78   10.338%   $254.638   $254.64   $254.65   $254.60  
  Purchase #3 $75.50   11.647%   $84.2935   $84.29   $84.30   $84.30  
  Purchase #4 $218.97   7.626%   $235.6687   $235.67   $235.65   $235.70  
  Purchase #5 $186.91   13.568%   $212.2699   $212.27   $212.25   $212.30  
  Purchase #6 $48.63   4.111%   $50.6292   $50.63   $50.65   $50.60  
  Purchase #7 $102.41   8.315%   $110.9254   $110.93   $110.95   $110.90  
  7 purchase totals = $930.66       $1,023.7903   $1,023.80   $1,023.80   $1,023.80