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	$34.91	7.745%	$37.6138	$37.61	$37.60	$37.60
Purchase #2	$122.31	11.690%	$136.608	$136.61	$136.60	$136.60
Purchase #3	$113.60	10.757%	$125.82	$125.82	$125.80	$125.80
Purchase #4	$18.25	13.558%	$20.7243	$20.72	$20.70	$20.70
Purchase #5	$115.26	12.451%	$129.611	$129.61	$129.60	$129.60
Purchase #6	$81.63	4.732%	$85.4927	$85.49	$85.50	$85.50
Purchase #7	$50.95	13.119%	$57.6341	$57.63	$57.65	$57.60
7 purchase totals =	$536.91		$593.5039	$593.49	$593.45	$593.40