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 $168.45   12.127%   $188.8779   $188.88   $188.90   $188.90  
  Purchase #2 $214.41   7.136%   $229.7103   $229.71   $229.70   $229.70  
  Purchase #3 $216.69   8.145%   $234.3394   $234.34   $234.35   $234.30  
  Purchase #4 $147.57   10.292%   $162.7579   $162.76   $162.75   $162.80  
  Purchase #5 $195.51   11.331%   $217.6632   $217.66   $217.65   $217.70  
  Purchase #6 $33.48   6.550%   $35.6729   $35.67   $35.65   $35.70  
  Purchase #7 $193.40   6.311%   $205.6055   $205.61   $205.60   $205.60  
  7 purchase totals = $1,169.51       $1,274.6271   $1,274.63   $1,274.60   $1,274.70