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	$164.83	3.547%	$170.6765	$170.68	$170.70	$170.70
Purchase #2	$100.74	9.208%	$110.0161	$110.02	$110.00	$110.00
Purchase #3	$200.38	12.292%	$225.0107	$225.01	$225.00	$225.00
Purchase #4	$145.34	3.841%	$150.9225	$150.92	$150.90	$150.90
Purchase #5	$93.32	9.413%	$102.1042	$102.10	$102.10	$102.10
Purchase #6	$172.51	10.429%	$190.5011	$190.50	$190.50	$190.50
Purchase #7	$49.89	6.746%	$53.2556	$53.26	$53.25	$53.30
7 purchase totals =	$927.01		$1,002.4867	$1,002.49	$1,002.45	$1,002.50