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	$147.81	12.127%	$165.7349	$165.73	$165.75	$165.70
Purchase #2	$22.60	12.256%	$25.3699	$25.37	$25.35	$25.40
Purchase #3	$232.91	9.498%	$255.0318	$255.03	$255.05	$255.00
Purchase #4	$83.37	7.325%	$89.4769	$89.48	$89.50	$89.50
Purchase #5	$140.96	3.139%	$145.3847	$145.38	$145.40	$145.40
Purchase #6	$50.92	6.730%	$54.3469	$54.35	$54.35	$54.30
Purchase #7	$71.59	4.310%	$74.6755	$74.68	$74.70	$74.70
7 purchase totals =	$750.16		$810.0206	$810.02	$810.10	$810.00