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 $59.31   11.591%   $66.1846   $66.18   $66.20   $66.20  
  Purchase #2 $110.43   7.129%   $118.3026   $118.30   $118.30   $118.30  
  Purchase #3 $141.57   9.460%   $154.9625   $154.96   $154.95   $155.00  
  Purchase #4 $95.83   11.681%   $107.0239   $107.02   $107.00   $107.00  
  Purchase #5 $162.71   8.694%   $176.856   $176.86   $176.85   $176.90  
  Purchase #6 $63.45   6.622%   $67.6517   $67.65   $67.65   $67.70  
  Purchase #7 $74.75   13.367%   $84.7418   $84.74   $84.75   $84.70  
  7 purchase totals = $708.05       $775.7231   $775.71   $775.70   $775.80