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 $76.92   8.182%   $83.2136   $83.21   $83.20   $83.20  
  Purchase #2 $175.84   11.442%   $195.9596   $195.96   $195.95   $196.00  
  Purchase #3 $119.42   6.561%   $127.2551   $127.26   $127.25   $127.30  
  Purchase #4 $67.95   4.652%   $71.111   $71.11   $71.10   $71.10  
  Purchase #5 $137.73   10.340%   $151.9713   $151.97   $151.95   $152.00  
  Purchase #6 $217.99   11.569%   $243.2093   $243.21   $243.20   $243.20  
  Purchase #7 $195.69   7.829%   $211.0106   $211.01   $211.00   $211.00  
  7 purchase totals = $991.54       $1,083.7305   $1,083.73   $1,083.65   $1,083.80