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	$151.92	8.816%	$165.3133	$165.31	$165.30	$165.30
Purchase #2	$115.55	4.574%	$120.8353	$120.84	$120.85	$120.80
Purchase #3	$230.41	5.843%	$243.8729	$243.87	$243.85	$243.90
Purchase #4	$40.61	11.811%	$45.4064	$45.41	$45.40	$45.40
Purchase #5	$27.34	4.287%	$28.5121	$28.51	$28.50	$28.50
Purchase #6	$17.56	4.824%	$18.4071	$18.41	$18.40	$18.40
Purchase #7	$210.73	8.533%	$228.7116	$228.71	$228.70	$228.70
7 purchase totals =	$794.12		$851.0587	$851.06	$851.00	$851.00