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 $57.42   9.297%   $62.7583   $62.76   $62.75   $62.80  
  Purchase #2 $127.94   10.394%   $141.2381   $141.24   $141.25   $141.20  
  Purchase #3 $118.99   6.109%   $126.2591   $126.26   $126.25   $126.30  
  Purchase #4 $217.25   11.516%   $242.2685   $242.27   $242.25   $242.30  
  Purchase #5 $215.73   5.226%   $227.004   $227.00   $227.00   $227.00  
  Purchase #6 $137.29   10.352%   $151.5023   $151.50   $151.50   $151.50  
  Purchase #7 $33.65   7.547%   $36.1896   $36.19   $36.20   $36.20  
  7 purchase totals = $908.27       $987.2199   $987.22   $987.20   $987.30