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 $68.98   10.776%   $76.4133   $76.41   $76.40   $76.40  
  Purchase #2 $183.73   11.163%   $204.2398   $204.24   $204.25   $204.20  
  Purchase #3 $203.42   9.370%   $222.4805   $222.48   $222.50   $222.50  
  Purchase #4 $194.68   10.257%   $214.6483   $214.65   $214.65   $214.60  
  Purchase #5 $70.81   3.866%   $73.5475   $73.55   $73.55   $73.50  
  Purchase #6 $233.40   3.211%   $240.8945   $240.89   $240.90   $240.90  
  Purchase #7 $204.89   10.550%   $226.5059   $226.51   $226.50   $226.50  
  7 purchase totals = $1,159.91       $1,258.7298   $1,258.73   $1,258.75   $1,258.60