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	$123.42	3.281%	$127.4694	$127.47	$127.45	$127.50
Purchase #2	$55.54	5.434%	$58.558	$58.56	$58.55	$58.60
Purchase #3	$79.48	13.846%	$90.4848	$90.48	$90.50	$90.50
Purchase #4	$16.86	7.679%	$18.1547	$18.15	$18.15	$18.20
Purchase #5	$164.29	3.645%	$170.2784	$170.28	$170.30	$170.30
Purchase #6	$53.32	7.444%	$57.2891	$57.29	$57.30	$57.30
Purchase #7	$249.30	8.737%	$271.0813	$271.08	$271.10	$271.10
7 purchase totals =	$742.21		$793.3157	$793.31	$793.35	$793.50