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 $190.94   5.387%   $201.2259   $201.23   $201.25   $201.20  
  Purchase #2 $60.73   10.127%   $66.8801   $66.88   $66.90   $66.90  
  Purchase #3 $20.54   11.774%   $22.9584   $22.96   $22.95   $23.00  
  Purchase #4 $13.38   8.836%   $14.5623   $14.56   $14.55   $14.60  
  Purchase #5 $182.52   8.807%   $198.5945   $198.59   $198.60   $198.60  
  Purchase #6 $64.88   7.191%   $69.5455   $69.55   $69.55   $69.50  
  Purchase #7 $148.60   8.652%   $161.4569   $161.46   $161.45   $161.50  
  7 purchase totals = $681.59       $735.2236   $735.23   $735.25   $735.30