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 $211.74   10.478%   $233.9261   $233.93   $233.95   $233.90  
  Purchase #2 $166.73   12.305%   $187.2461   $187.25   $187.25   $187.20  
  Purchase #3 $181.76   9.401%   $198.8473   $198.85   $198.85   $198.80  
  Purchase #4 $187.72   11.384%   $209.09   $209.09   $209.10   $209.10  
  Purchase #5 $218.67   4.177%   $227.8038   $227.80   $227.80   $227.80  
  Purchase #6 $236.63   10.571%   $261.6442   $261.64   $261.65   $261.60  
  Purchase #7 $43.89   10.263%   $48.3944   $48.39   $48.40   $48.40  
  7 purchase totals = $1,247.14       $1,366.9519   $1,366.95   $1,367.00   $1,366.80