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 $244.34   9.205%   $266.8315   $266.83   $266.85   $266.80  
  Purchase #2 $118.57   7.334%   $127.2659   $127.27   $127.25   $127.30  
  Purchase #3 $43.84   10.693%   $48.5278   $48.53   $48.55   $48.50  
  Purchase #4 $219.58   12.191%   $246.349   $246.35   $246.35   $246.30  
  Purchase #5 $141.76   5.625%   $149.734   $149.73   $149.75   $149.70  
  Purchase #6 $229.94   9.118%   $250.9059   $250.91   $250.90   $250.90  
  Purchase #7 $236.37   10.579%   $261.3756   $261.38   $261.40   $261.40  
  7 purchase totals = $1,234.40       $1,350.9897   $1,351.00   $1,351.05   $1,350.90