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 $219.94   12.202%   $246.7771   $246.78   $246.80   $246.80  
  Purchase #2 $233.76   11.645%   $260.9814   $260.98   $261.00   $261.00  
  Purchase #3 $236.62   9.627%   $259.3994   $259.40   $259.40   $259.40  
  Purchase #4 $169.87   10.291%   $187.3513   $187.35   $187.35   $187.40  
  Purchase #5 $87.97   12.355%   $98.8387   $98.84   $98.85   $98.80  
  Purchase #6 $150.63   8.642%   $163.6474   $163.65   $163.65   $163.60  
  Purchase #7 $195.90   10.555%   $216.5772   $216.58   $216.60   $216.60  
  7 purchase totals = $1,294.69       $1,433.5725   $1,433.58   $1,433.65   $1,433.60