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 $204.97   10.562%   $226.6189   $226.62   $226.60   $226.60  
  Purchase #2 $172.51   7.471%   $185.3982   $185.40   $185.40   $185.40  
  Purchase #3 $131.48   5.249%   $138.3814   $138.38   $138.40   $138.40  
  Purchase #4 $68.90   12.136%   $77.2617   $77.26   $77.25   $77.30  
  Purchase #5 $48.33   11.153%   $53.7202   $53.72   $53.70   $53.70  
  Purchase #6 $188.96   6.545%   $201.3274   $201.33   $201.35   $201.30  
  Purchase #7 $49.98   6.362%   $53.1597   $53.16   $53.15   $53.20  
  7 purchase totals = $865.13       $935.8675   $935.87   $935.85   $935.90