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 $34.29   3.512%   $35.4943   $35.49   $35.50   $35.50  
  Purchase #2 $105.97   7.172%   $113.5702   $113.57   $113.55   $113.60  
  Purchase #3 $126.41   12.647%   $142.3971   $142.40   $142.40   $142.40  
  Purchase #4 $206.75   12.358%   $232.3002   $232.30   $232.30   $232.30  
  Purchase #5 $78.40   11.483%   $87.4027   $87.40   $87.40   $87.40  
  Purchase #6 $107.44   10.785%   $119.0274   $119.03   $119.05   $119.00  
  Purchase #7 $61.76   5.416%   $65.1049   $65.10   $65.10   $65.10  
  7 purchase totals = $721.02       $795.2968   $795.29   $795.30   $795.30