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 $101.58   3.863%   $105.504   $105.50   $105.50   $105.50  
  Purchase #2 $113.48   12.594%   $127.7717   $127.77   $127.75   $127.80  
  Purchase #3 $6.72   13.583%   $7.6328   $7.63   $7.65   $7.60  
  Purchase #4 $166.95   3.745%   $173.2023   $173.20   $173.20   $173.20  
  Purchase #5 $183.77   5.627%   $194.1107   $194.11   $194.10   $194.10  
  Purchase #6 $236.77   11.417%   $263.802   $263.80   $263.80   $263.80  
  Purchase #7 $77.50   7.191%   $83.073   $83.07   $83.05   $83.10  
  7 purchase totals = $886.77       $955.0965   $955.08   $955.05   $955.10