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 $59.77   8.370%   $64.7727   $64.77   $64.75   $64.80  
  Purchase #2 $11.63   12.551%   $13.0897   $13.09   $13.10   $13.10  
  Purchase #3 $19.79   12.487%   $22.2612   $22.26   $22.25   $22.30  
  Purchase #4 $119.95   8.462%   $130.1002   $130.10   $130.10   $130.10  
  Purchase #5 $147.25   13.166%   $166.6369   $166.64   $166.65   $166.60  
  Purchase #6 $245.60   5.671%   $259.528   $259.53   $259.55   $259.50  
  Purchase #7 $108.63   9.174%   $118.5957   $118.60   $118.60   $118.60  
  7 purchase totals = $712.62       $774.9844   $774.99   $775.00   $775.00