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	$32.37	7.719%	$34.8686	$34.87	$34.85	$34.90
Purchase #2	$100.29	9.246%	$109.5628	$109.56	$109.55	$109.60
Purchase #3	$58.93	3.349%	$60.9036	$60.90	$60.90	$60.90
Purchase #4	$10.59	13.583%	$12.0284	$12.03	$12.05	$12.00
Purchase #5	$67.28	6.276%	$71.5025	$71.50	$71.50	$71.50
Purchase #6	$202.48	11.502%	$225.7692	$225.77	$225.75	$225.80
Purchase #7	$117.72	8.684%	$127.9428	$127.94	$127.95	$127.90
7 purchase totals =	$589.66		$642.5779	$642.57	$642.55	$642.60