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 $216.53   9.154%   $236.3512   $236.35   $236.35   $236.40  
  Purchase #2 $61.59   3.186%   $63.5523   $63.55   $63.55   $63.60  
  Purchase #3 $238.30   10.773%   $263.9721   $263.97   $263.95   $264.00  
  Purchase #4 $250.86   6.783%   $267.8758   $267.88   $267.90   $267.90  
  Purchase #5 $100.95   6.411%   $107.4219   $107.42   $107.40   $107.40  
  Purchase #6 $231.49   11.711%   $258.5998   $258.60   $258.60   $258.60  
  Purchase #7 $101.29   8.361%   $109.7589   $109.76   $109.75   $109.80  
  7 purchase totals = $1,201.01       $1,307.5320   $1,307.53   $1,307.50   $1,307.70