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 $219.39   11.681%   $245.0169   $245.02   $245.00   $245.00  
  Purchase #2 $115.60   9.614%   $126.7138   $126.71   $126.70   $126.70  
  Purchase #3 $10.36   13.667%   $11.7759   $11.78   $11.80   $11.80  
  Purchase #4 $224.33   12.246%   $251.8015   $251.80   $251.80   $251.80  
  Purchase #5 $48.99   11.729%   $54.736   $54.74   $54.75   $54.70  
  Purchase #6 $121.60   3.589%   $125.9642   $125.96   $125.95   $126.00  
  Purchase #7 $197.34   5.384%   $207.9648   $207.96   $207.95   $208.00  
  7 purchase totals = $937.61       $1,023.9731   $1,023.97   $1,023.95   $1,024.00