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 $151.66   11.842%   $169.6196   $169.62   $169.60   $169.60  
  Purchase #2 $14.85   4.629%   $15.5374   $15.54   $15.55   $15.50  
  Purchase #3 $101.69   5.441%   $107.223   $107.22   $107.20   $107.20  
  Purchase #4 $193.63   8.579%   $210.2415   $210.24   $210.25   $210.20  
  Purchase #5 $114.46   6.162%   $121.513   $121.51   $121.50   $121.50  
  Purchase #6 $72.95   5.418%   $76.9024   $76.90   $76.90   $76.90  
  Purchase #7 $199.34   13.331%   $225.914   $225.91   $225.90   $225.90  
  7 purchase totals = $848.58       $926.9509   $926.94   $926.90   $926.80