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 $229.86   6.427%   $244.6331   $244.63   $244.65   $244.60  
  Purchase #2 $31.98   11.321%   $35.6005   $35.60   $35.60   $35.60  
  Purchase #3 $68.32   9.149%   $74.5706   $74.57   $74.55   $74.60  
  Purchase #4 $192.76   10.256%   $212.5295   $212.53   $212.55   $212.50  
  Purchase #5 $82.91   11.371%   $92.3377   $92.34   $92.35   $92.30  
  Purchase #6 $167.90   8.729%   $182.556   $182.56   $182.55   $182.60  
  Purchase #7 $129.41   8.678%   $140.6402   $140.64   $140.65   $140.60  
  7 purchase totals = $903.14       $982.8676   $982.87   $982.90   $982.80