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	$80.77	11.851%	$90.3421	$90.34	$90.35	$90.30
Purchase #2	$223.89	13.583%	$254.301	$254.30	$254.30	$254.30
Purchase #3	$27.70	6.479%	$29.4947	$29.49	$29.50	$29.50
Purchase #4	$243.83	11.483%	$271.829	$271.83	$271.85	$271.80
Purchase #5	$79.74	10.849%	$88.391	$88.39	$88.40	$88.40
Purchase #6	$99.28	7.318%	$106.5453	$106.55	$106.55	$106.50
Purchase #7	$45.30	12.714%	$51.0594	$51.06	$51.05	$51.10
7 purchase totals =	$800.51		$891.9625	$891.96	$892.00	$891.90