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	$100.35	3.383%	$103.7448	$103.74	$103.75	$103.70
Purchase #2	$49.95	7.206%	$53.5494	$53.55	$53.55	$53.50
Purchase #3	$58.29	13.759%	$66.3101	$66.31	$66.30	$66.30
Purchase #4	$98.95	4.427%	$103.3305	$103.33	$103.35	$103.30
Purchase #5	$30.87	13.365%	$34.9958	$35.00	$35.00	$35.00
Purchase #6	$75.59	6.183%	$80.2637	$80.26	$80.25	$80.30
Purchase #7	$179.51	11.835%	$200.755	$200.76	$200.75	$200.80
7 purchase totals =	$593.51		$642.9493	$642.95	$642.95	$642.90