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 $240.43   5.468%   $253.5767   $253.58   $253.60   $253.60  
  Purchase #2 $238.66   9.443%   $261.1967   $261.20   $261.20   $261.20  
  Purchase #3 $44.29   9.144%   $48.3399   $48.34   $48.35   $48.30  
  Purchase #4 $78.92   5.775%   $83.4776   $83.48   $83.50   $83.50  
  Purchase #5 $113.33   11.633%   $126.5137   $126.51   $126.50   $126.50  
  Purchase #6 $88.33   11.683%   $98.6496   $98.65   $98.65   $98.60  
  Purchase #7 $190.40   11.675%   $212.6292   $212.63   $212.65   $212.60  
  7 purchase totals = $994.36       $1,084.3834   $1,084.39   $1,084.45   $1,084.30