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 $176.69   10.456%   $195.1647   $195.16   $195.15   $195.20  
  Purchase #2 $120.92   12.432%   $135.9528   $135.95   $135.95   $136.00  
  Purchase #3 $131.27   11.236%   $146.0195   $146.02   $146.00   $146.00  
  Purchase #4 $57.67   8.251%   $62.4284   $62.43   $62.45   $62.40  
  Purchase #5 $111.86   8.590%   $121.4688   $121.47   $121.45   $121.50  
  Purchase #6 $146.35   13.670%   $166.356   $166.36   $166.35   $166.40  
  Purchase #7 $160.68   4.766%   $168.338   $168.34   $168.35   $168.30  
  7 purchase totals = $905.44       $995.7282   $995.73   $995.70   $995.80