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	$137.84	10.110%	$151.7756	$151.78	$151.80	$151.80
Purchase #2	$98.54	10.348%	$108.7369	$108.74	$108.75	$108.70
Purchase #3	$156.50	7.388%	$168.0622	$168.06	$168.05	$168.10
Purchase #4	$9.64	9.489%	$10.5547	$10.55	$10.55	$10.60
Purchase #5	$72.67	6.154%	$77.1421	$77.14	$77.15	$77.10
Purchase #6	$168.55	11.679%	$188.235	$188.24	$188.25	$188.20
Purchase #7	$101.56	3.814%	$105.4335	$105.43	$105.45	$105.40
7 purchase totals =	$745.30		$809.9400	$809.94	$810.00	$809.90