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 $33.61   3.443%   $34.7672   $34.77   $34.75   $34.80  
  Purchase #2 $167.36   11.517%   $186.6349   $186.63   $186.65   $186.60  
  Purchase #3 $157.51   3.152%   $162.4747   $162.47   $162.45   $162.50  
  Purchase #4 $161.65   9.397%   $176.8403   $176.84   $176.85   $176.80  
  Purchase #5 $90.31   13.539%   $102.5371   $102.54   $102.55   $102.50  
  Purchase #6 $244.37   12.384%   $274.6328   $274.63   $274.65   $274.60  
  Purchase #7 $126.39   9.110%   $137.9041   $137.90   $137.90   $137.90  
  7 purchase totals = $981.20       $1,075.7911   $1,075.78   $1,075.80   $1,075.70