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	$35.98	4.765%	$37.6944	$37.69	$37.70	$37.70
Purchase #2	$191.92	11.760%	$214.4898	$214.49	$214.50	$214.50
Purchase #3	$95.69	5.477%	$100.9309	$100.93	$100.95	$100.90
Purchase #4	$213.33	7.805%	$229.9804	$229.98	$230.00	$230.00
Purchase #5	$10.95	10.117%	$12.0578	$12.06	$12.05	$12.10
Purchase #6	$132.41	3.561%	$137.1251	$137.13	$137.15	$137.10
Purchase #7	$99.58	7.746%	$107.2935	$107.29	$107.30	$107.30
7 purchase totals =	$779.86		$839.5719	$839.57	$839.65	$839.60