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 $58.49   12.763%   $65.9551   $65.96   $65.95   $66.00  
  Purchase #2 $216.31   6.129%   $229.5676   $229.57   $229.55   $229.60  
  Purchase #3 $146.46   9.355%   $160.1613   $160.16   $160.15   $160.20  
  Purchase #4 $123.28   3.574%   $127.686   $127.69   $127.70   $127.70  
  Purchase #5 $202.35   3.235%   $208.896   $208.90   $208.90   $208.90  
  Purchase #6 $118.64   8.764%   $129.0376   $129.04   $129.05   $129.00  
  Purchase #7 $19.74   6.819%   $21.0861   $21.09   $21.10   $21.10  
  7 purchase totals = $885.27       $942.3897   $942.41   $942.40   $942.50