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 $191.89   5.837%   $203.0906   $203.09   $203.10   $203.10  
  Purchase #2 $243.91   11.199%   $271.2255   $271.23   $271.25   $271.20  
  Purchase #3 $68.52   11.434%   $76.3546   $76.35   $76.35   $76.40  
  Purchase #4 $207.83   4.327%   $216.8228   $216.82   $216.80   $216.80  
  Purchase #5 $156.94   11.169%   $174.4686   $174.47   $174.45   $174.50  
  Purchase #6 $65.74   5.697%   $69.4852   $69.49   $69.50   $69.50  
  Purchase #7 $182.60   6.795%   $195.0077   $195.01   $195.00   $195.00  
  7 purchase totals = $1,117.43       $1,206.4550   $1,206.46   $1,206.45   $1,206.50