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 $142.83   13.396%   $161.9635   $161.96   $161.95   $162.00  
  Purchase #2 $122.43   9.447%   $133.996   $134.00   $134.00   $134.00  
  Purchase #3 $62.47   6.652%   $66.6255   $66.63   $66.65   $66.60  
  Purchase #4 $234.44   4.657%   $245.3579   $245.36   $245.35   $245.40  
  Purchase #5 $134.67   12.354%   $151.3071   $151.31   $151.30   $151.30  
  Purchase #6 $133.49   3.229%   $137.8004   $137.80   $137.80   $137.80  
  Purchase #7 $211.31   7.258%   $226.6469   $226.65   $226.65   $226.60  
  7 purchase totals = $1,041.64       $1,123.6973   $1,123.71   $1,123.70   $1,123.70