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 $245.72   12.530%   $276.5087   $276.51   $276.50   $276.50  
  Purchase #2 $89.71   3.504%   $92.8534   $92.85   $92.85   $92.90  
  Purchase #3 $50.78   6.290%   $53.9741   $53.97   $53.95   $54.00  
  Purchase #4 $227.68   11.838%   $254.6328   $254.63   $254.65   $254.60  
  Purchase #5 $213.99   13.661%   $243.2232   $243.22   $243.20   $243.20  
  Purchase #6 $10.78   3.765%   $11.1859   $11.19   $11.20   $11.20  
  Purchase #7 $87.47   13.449%   $99.2338   $99.23   $99.25   $99.20  
  7 purchase totals = $926.13       $1,031.6119   $1,031.60   $1,031.60   $1,031.60