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 $202.82   11.676%   $226.5013   $226.50   $226.50   $226.50  
  Purchase #2 $90.70   4.686%   $94.9502   $94.95   $94.95   $95.00  
  Purchase #3 $107.63   10.258%   $118.6707   $118.67   $118.65   $118.70  
  Purchase #4 $190.74   8.396%   $206.7545   $206.75   $206.75   $206.80  
  Purchase #5 $20.48   8.833%   $22.289   $22.29   $22.30   $22.30  
  Purchase #6 $15.61   13.176%   $17.6668   $17.67   $17.65   $17.70  
  Purchase #7 $199.61   9.310%   $218.1937   $218.19   $218.20   $218.20  
  7 purchase totals = $827.59       $905.0262   $905.02   $905.00   $905.20