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 $58.42   3.669%   $60.5634   $60.56   $60.55   $60.60  
  Purchase #2 $195.36   10.777%   $216.4139   $216.41   $216.40   $216.40  
  Purchase #3 $187.37   3.216%   $193.3958   $193.40   $193.40   $193.40  
  Purchase #4 $250.96   8.288%   $271.7596   $271.76   $271.75   $271.80  
  Purchase #5 $46.33   3.497%   $47.9502   $47.95   $47.95   $48.00  
  Purchase #6 $47.85   8.109%   $51.7302   $51.73   $51.75   $51.70  
  Purchase #7 $51.54   5.295%   $54.269   $54.27   $54.25   $54.30  
  7 purchase totals = $837.83       $896.0821   $896.08   $896.05   $896.20