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 $151.87   8.853%   $165.3151   $165.32   $165.30   $165.30  
  Purchase #2 $43.84   6.115%   $46.5208   $46.52   $46.50   $46.50  
  Purchase #3 $101.68   12.855%   $114.751   $114.75   $114.75   $114.80  
  Purchase #4 $248.33   4.276%   $258.9486   $258.95   $258.95   $258.90  
  Purchase #5 $73.86   3.795%   $76.663   $76.66   $76.65   $76.70  
  Purchase #6 $78.64   4.550%   $82.2181   $82.22   $82.20   $82.20  
  Purchase #7 $157.47   3.365%   $162.7689   $162.77   $162.75   $162.80  
  7 purchase totals = $855.69       $907.1855   $907.19   $907.10   $907.20