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 $208.98   8.180%   $226.0746   $226.07   $226.05   $226.10  
  Purchase #2 $218.50   6.612%   $232.9472   $232.95   $232.95   $232.90  
  Purchase #3 $213.81   11.221%   $237.8016   $237.80   $237.80   $237.80  
  Purchase #4 $92.68   4.686%   $97.023   $97.02   $97.00   $97.00  
  Purchase #5 $154.51   13.279%   $175.0274   $175.03   $175.05   $175.00  
  Purchase #6 $94.63   13.557%   $107.459   $107.46   $107.45   $107.50  
  Purchase #7 $233.98   7.464%   $251.4443   $251.44   $251.45   $251.40  
  7 purchase totals = $1,217.09       $1,327.7771   $1,327.77   $1,327.75   $1,327.70