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 $221.73   9.130%   $241.9739   $241.97   $241.95   $242.00  
  Purchase #2 $194.96   11.143%   $216.6844   $216.68   $216.70   $216.70  
  Purchase #3 $247.94   11.306%   $275.9721   $275.97   $275.95   $276.00  
  Purchase #4 $78.81   10.829%   $87.3443   $87.34   $87.35   $87.30  
  Purchase #5 $217.97   12.834%   $245.9443   $245.94   $245.95   $245.90  
  Purchase #6 $219.34   9.108%   $239.3175   $239.32   $239.30   $239.30  
  Purchase #7 $182.87   11.544%   $203.9805   $203.98   $204.00   $204.00  
  7 purchase totals = $1,363.62       $1,511.2170   $1,511.20   $1,511.20   $1,511.20