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 $114.39   4.278%   $119.2836   $119.28   $119.30   $119.30  
  Purchase #2 $74.62   13.475%   $84.675   $84.68   $84.70   $84.70  
  Purchase #3 $112.35   8.464%   $121.8593   $121.86   $121.85   $121.90  
  Purchase #4 $25.26   7.364%   $27.1201   $27.12   $27.10   $27.10  
  Purchase #5 $229.36   5.565%   $242.1239   $242.12   $242.10   $242.10  
  Purchase #6 $185.68   7.717%   $200.0089   $200.01   $200.00   $200.00  
  Purchase #7 $182.95   12.631%   $206.0584   $206.06   $206.05   $206.10  
  7 purchase totals = $924.61       $1,001.1292   $1,001.13   $1,001.10   $1,001.20