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 $5.50   4.304%   $5.7367   $5.74   $5.75   $5.70  
  Purchase #2 $81.36   3.801%   $84.4525   $84.45   $84.45   $84.50  
  Purchase #3 $43.34   7.716%   $46.6841   $46.68   $46.70   $46.70  
  Purchase #4 $113.74   9.867%   $124.9627   $124.96   $124.95   $125.00  
  Purchase #5 $28.43   5.692%   $30.0482   $30.05   $30.05   $30.00  
  Purchase #6 $133.51   13.640%   $151.7208   $151.72   $151.70   $151.70  
  Purchase #7 $43.38   8.209%   $46.9411   $46.94   $46.95   $46.90  
  7 purchase totals = $449.26       $490.5461   $490.54   $490.55   $490.50