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 $84.41   9.420%   $92.3614   $92.36   $92.35   $92.40  
  Purchase #2 $20.78   10.669%   $22.997   $23.00   $23.00   $23.00  
  Purchase #3 $162.38   3.832%   $168.6024   $168.60   $168.60   $168.60  
  Purchase #4 $182.85   7.651%   $196.8399   $196.84   $196.85   $196.80  
  Purchase #5 $110.96   7.397%   $119.1677   $119.17   $119.15   $119.20  
  Purchase #6 $245.60   11.176%   $273.0483   $273.05   $273.05   $273.00  
  Purchase #7 $166.73   8.327%   $180.6136   $180.61   $180.60   $180.60  
  7 purchase totals = $973.71       $1,053.6303   $1,053.63   $1,053.60   $1,053.60