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	$31.38	7.767%	$33.8173	$33.82	$33.80	$33.80
Purchase #2	$133.95	4.569%	$140.0702	$140.07	$140.05	$140.10
Purchase #3	$21.73	7.546%	$23.3697	$23.37	$23.35	$23.40
Purchase #4	$121.40	12.645%	$136.751	$136.75	$136.75	$136.80
Purchase #5	$78.52	5.179%	$82.5866	$82.59	$82.60	$82.60
Purchase #6	$71.32	3.221%	$73.6172	$73.62	$73.60	$73.60
Purchase #7	$72.58	11.359%	$80.8244	$80.82	$80.80	$80.80
7 purchase totals =	$530.88		$571.0364	$571.04	$570.95	$571.10