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 $178.61   3.758%   $185.3222   $185.32   $185.30   $185.30  
  Purchase #2 $185.78   3.455%   $192.1987   $192.20   $192.20   $192.20  
  Purchase #3 $236.48   8.253%   $255.9967   $256.00   $256.00   $256.00  
  Purchase #4 $48.26   10.721%   $53.434   $53.43   $53.45   $53.40  
  Purchase #5 $60.49   12.278%   $67.917   $67.92   $67.90   $67.90  
  Purchase #6 $92.54   6.122%   $98.2053   $98.21   $98.20   $98.20  
  Purchase #7 $134.58   10.807%   $149.1241   $149.12   $149.10   $149.10  
  7 purchase totals = $936.74       $1,002.1980   $1,002.20   $1,002.15   $1,002.10