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 $196.56   9.293%   $214.8263   $214.83   $214.85   $214.80  
  Purchase #2 $249.46   8.194%   $269.9008   $269.90   $269.90   $269.90  
  Purchase #3 $64.50   7.690%   $69.4601   $69.46   $69.45   $69.50  
  Purchase #4 $202.48   7.305%   $217.2712   $217.27   $217.25   $217.30  
  Purchase #5 $104.90   13.207%   $118.7541   $118.75   $118.75   $118.80  
  Purchase #6 $27.66   7.603%   $29.763   $29.76   $29.75   $29.80  
  Purchase #7 $192.48   8.262%   $208.3827   $208.38   $208.40   $208.40  
  7 purchase totals = $1,038.04       $1,128.3582   $1,128.35   $1,128.35   $1,128.50