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 $205.53   5.791%   $217.4322   $217.43   $217.45   $217.40  
  Purchase #2 $138.68   10.595%   $153.3731   $153.37   $153.35   $153.40  
  Purchase #3 $216.87   8.785%   $235.922   $235.92   $235.90   $235.90  
  Purchase #4 $236.75   9.853%   $260.077   $260.08   $260.10   $260.10  
  Purchase #5 $224.29   3.435%   $231.9944   $231.99   $232.00   $232.00  
  Purchase #6 $131.90   3.363%   $136.3358   $136.34   $136.35   $136.30  
  Purchase #7 $123.62   6.822%   $132.0534   $132.05   $132.05   $132.10  
  7 purchase totals = $1,277.64       $1,367.1879   $1,367.18   $1,367.20   $1,367.20