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	$150.45	3.329%	$155.4585	$155.46	$155.45	$155.50
Purchase #2	$39.47	3.637%	$40.9055	$40.91	$40.90	$40.90
Purchase #3	$238.72	6.768%	$254.8766	$254.88	$254.90	$254.90
Purchase #4	$27.39	7.825%	$29.5333	$29.53	$29.55	$29.50
Purchase #5	$77.69	6.480%	$82.7243	$82.72	$82.70	$82.70
Purchase #6	$11.59	4.696%	$12.1343	$12.13	$12.15	$12.10
Purchase #7	$20.73	13.668%	$23.5634	$23.56	$23.55	$23.60
7 purchase totals =	$566.04		$599.1959	$599.19	$599.20	$599.20