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 $112.53   13.634%   $127.8723   $127.87   $127.85   $127.90  
  Purchase #2 $215.48   5.344%   $226.9953   $227.00   $227.00   $227.00  
  Purchase #3 $54.41   11.587%   $60.7145   $60.71   $60.70   $60.70  
  Purchase #4 $87.70   12.814%   $98.9379   $98.94   $98.95   $98.90  
  Purchase #5 $68.93   13.296%   $78.0949   $78.09   $78.10   $78.10  
  Purchase #6 $115.60   9.128%   $126.152   $126.15   $126.15   $126.20  
  Purchase #7 $249.29   10.640%   $275.8145   $275.81   $275.80   $275.80  
  7 purchase totals = $903.94       $994.5814   $994.57   $994.55   $994.60