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 $164.63   3.271%   $170.015   $170.02   $170.00   $170.00  
  Purchase #2 $5.55   8.151%   $6.0024   $6.00   $6.00   $6.00  
  Purchase #3 $74.85   9.697%   $82.1082   $82.11   $82.10   $82.10  
  Purchase #4 $214.26   9.659%   $234.9554   $234.96   $234.95   $235.00  
  Purchase #5 $161.69   6.829%   $172.7318   $172.73   $172.75   $172.70  
  Purchase #6 $61.80   4.362%   $64.4957   $64.50   $64.50   $64.50  
  Purchase #7 $216.88   9.185%   $236.8004   $236.80   $236.80   $236.80  
  7 purchase totals = $899.66       $967.1089   $967.12   $967.10   $967.10