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 $94.87   3.542%   $98.2303   $98.23   $98.25   $98.20  
  Purchase #2 $248.88   7.323%   $267.1055   $267.11   $267.10   $267.10  
  Purchase #3 $46.65   10.684%   $51.6341   $51.63   $51.65   $51.60  
  Purchase #4 $232.75   9.196%   $254.1537   $254.15   $254.15   $254.20  
  Purchase #5 $129.29   7.618%   $139.1393   $139.14   $139.15   $139.10  
  Purchase #6 $80.83   8.834%   $87.9705   $87.97   $87.95   $88.00  
  Purchase #7 $57.38   8.658%   $62.348   $62.35   $62.35   $62.30  
  7 purchase totals = $890.65       $960.5814   $960.58   $960.60   $960.50