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 $207.95   11.313%   $231.4754   $231.48   $231.50   $231.50  
  Purchase #2 $99.85   13.426%   $113.2559   $113.26   $113.25   $113.30  
  Purchase #3 $22.93   5.343%   $24.1551   $24.16   $24.15   $24.20  
  Purchase #4 $139.56   10.450%   $154.144   $154.14   $154.15   $154.10  
  Purchase #5 $232.37   12.323%   $261.005   $261.01   $261.00   $261.00  
  Purchase #6 $48.77   9.200%   $53.2568   $53.26   $53.25   $53.30  
  Purchase #7 $10.79   7.853%   $11.6373   $11.64   $11.65   $11.60  
  7 purchase totals = $762.22       $848.9295   $848.95   $848.95   $849.00