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 $200.32   12.297%   $224.9534   $224.95   $224.95   $225.00  
  Purchase #2 $68.41   10.303%   $75.4583   $75.46   $75.45   $75.50  
  Purchase #3 $120.35   11.616%   $134.3299   $134.33   $134.35   $134.30  
  Purchase #4 $112.75   7.741%   $121.478   $121.48   $121.50   $121.50  
  Purchase #5 $167.66   9.237%   $183.1468   $183.15   $183.15   $183.10  
  Purchase #6 $47.71   4.114%   $49.6728   $49.67   $49.65   $49.70  
  Purchase #7 $225.27   4.265%   $234.8778   $234.88   $234.90   $234.90  
  7 purchase totals = $942.47       $1,023.9170   $1,023.92   $1,023.95   $1,024.00