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 $44.82   3.293%   $46.2959   $46.30   $46.30   $46.30  
  Purchase #2 $112.96   13.182%   $127.8504   $127.85   $127.85   $127.90  
  Purchase #3 $23.29   12.354%   $26.1672   $26.17   $26.15   $26.20  
  Purchase #4 $70.38   8.528%   $76.382   $76.38   $76.40   $76.40  
  Purchase #5 $143.94   8.580%   $156.2901   $156.29   $156.30   $156.30  
  Purchase #6 $19.92   5.477%   $21.011   $21.01   $21.00   $21.00  
  Purchase #7 $199.46   6.286%   $211.9981   $212.00   $212.00   $212.00  
  7 purchase totals = $614.77       $665.9947   $666.00   $666.00   $666.10