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 $69.79   13.570%   $79.2605   $79.26   $79.25   $79.30  
  Purchase #2 $87.28   10.667%   $96.5902   $96.59   $96.60   $96.60  
  Purchase #3 $59.43   12.556%   $66.892   $66.89   $66.90   $66.90  
  Purchase #4 $191.29   8.278%   $207.125   $207.13   $207.15   $207.10  
  Purchase #5 $213.25   11.118%   $236.9591   $236.96   $236.95   $237.00  
  Purchase #6 $140.86   10.808%   $156.0841   $156.08   $156.10   $156.10  
  Purchase #7 $82.88   11.176%   $92.1427   $92.14   $92.15   $92.10  
  7 purchase totals = $844.78       $935.0536   $935.05   $935.10   $935.10