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 $241.93   5.582%   $255.4345   $255.43   $255.45   $255.40  
  Purchase #2 $190.96   11.381%   $212.6932   $212.69   $212.70   $212.70  
  Purchase #3 $106.28   12.549%   $119.6171   $119.62   $119.60   $119.60  
  Purchase #4 $136.36   9.221%   $148.9338   $148.93   $148.95   $148.90  
  Purchase #5 $14.57   8.339%   $15.785   $15.79   $15.80   $15.80  
  Purchase #6 $229.91   12.162%   $257.8717   $257.87   $257.85   $257.90  
  Purchase #7 $217.44   7.618%   $234.0046   $234.00   $234.00   $234.00  
  7 purchase totals = $1,137.45       $1,244.3399   $1,244.33   $1,244.35   $1,244.30