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 $237.80   10.770%   $263.4111   $263.41   $263.40   $263.40  
  Purchase #2 $104.89   13.141%   $118.6736   $118.67   $118.65   $118.70  
  Purchase #3 $208.52   12.200%   $233.9594   $233.96   $233.95   $234.00  
  Purchase #4 $14.97   3.282%   $15.4613   $15.46   $15.45   $15.50  
  Purchase #5 $107.26   7.708%   $115.5276   $115.53   $115.55   $115.50  
  Purchase #6 $79.57   5.622%   $84.0434   $84.04   $84.05   $84.00  
  Purchase #7 $198.99   8.359%   $215.6236   $215.62   $215.60   $215.60  
  7 purchase totals = $952.00       $1,046.7000   $1,046.69   $1,046.65   $1,046.70