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 $194.62   9.155%   $212.4375   $212.44   $212.45   $212.40  
  Purchase #2 $33.87   4.239%   $35.3057   $35.31   $35.30   $35.30  
  Purchase #3 $34.28   9.735%   $37.6172   $37.62   $37.60   $37.60  
  Purchase #4 $153.97   8.437%   $166.9604   $166.96   $166.95   $167.00  
  Purchase #5 $63.74   13.180%   $72.1409   $72.14   $72.15   $72.10  
  Purchase #6 $95.58   11.126%   $106.2142   $106.21   $106.20   $106.20  
  Purchase #7 $177.63   4.685%   $185.952   $185.95   $185.95   $186.00  
  7 purchase totals = $753.69       $816.6279   $816.63   $816.60   $816.60