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 $201.69   10.180%   $222.222   $222.22   $222.20   $222.20  
  Purchase #2 $174.48   4.218%   $181.8396   $181.84   $181.85   $181.80  
  Purchase #3 $45.33   8.355%   $49.1173   $49.12   $49.10   $49.10  
  Purchase #4 $148.99   7.233%   $159.7664   $159.77   $159.75   $159.80  
  Purchase #5 $245.55   9.146%   $268.008   $268.01   $268.00   $268.00  
  Purchase #6 $14.64   13.858%   $16.6688   $16.67   $16.65   $16.70  
  Purchase #7 $67.75   13.185%   $76.6828   $76.68   $76.70   $76.70  
  7 purchase totals = $898.43       $974.3049   $974.31   $974.25   $974.30