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 $232.98   6.536%   $248.2076   $248.21   $248.20   $248.20  
  Purchase #2 $76.85   13.138%   $86.9466   $86.95   $86.95   $86.90  
  Purchase #3 $203.79   8.263%   $220.6292   $220.63   $220.65   $220.60  
  Purchase #4 $246.84   9.565%   $270.4502   $270.45   $270.45   $270.50  
  Purchase #5 $15.44   3.259%   $15.9432   $15.94   $15.95   $15.90  
  Purchase #6 $15.25   10.766%   $16.8918   $16.89   $16.90   $16.90  
  Purchase #7 $184.86   6.150%   $196.2289   $196.23   $196.25   $196.20  
  7 purchase totals = $976.01       $1,055.2975   $1,055.30   $1,055.35   $1,055.20