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 $233.70   11.666%   $260.9634   $260.96   $260.95   $261.00  
  Purchase #2 $204.63   8.182%   $221.3728   $221.37   $221.35   $221.40  
  Purchase #3 $125.51   6.835%   $134.0886   $134.09   $134.10   $134.10  
  Purchase #4 $43.53   7.446%   $46.7712   $46.77   $46.75   $46.80  
  Purchase #5 $61.53   8.409%   $66.7041   $66.70   $66.70   $66.70  
  Purchase #6 $14.99   5.204%   $15.7701   $15.77   $15.75   $15.80  
  Purchase #7 $249.71   10.362%   $275.585   $275.59   $275.60   $275.60  
  7 purchase totals = $933.60       $1,021.2552   $1,021.25   $1,021.20   $1,021.40