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 $34.85   10.255%   $38.4239   $38.42   $38.40   $38.40  
  Purchase #2 $98.88   4.723%   $103.5501   $103.55   $103.55   $103.60  
  Purchase #3 $66.95   13.551%   $76.0224   $76.02   $76.00   $76.00  
  Purchase #4 $175.41   6.848%   $187.4221   $187.42   $187.40   $187.40  
  Purchase #5 $158.85   13.516%   $180.3202   $180.32   $180.30   $180.30  
  Purchase #6 $226.93   4.566%   $237.2916   $237.29   $237.30   $237.30  
  Purchase #7 $189.36   5.374%   $199.5362   $199.54   $199.55   $199.50  
  7 purchase totals = $951.23       $1,022.5665   $1,022.56   $1,022.50   $1,022.50