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	$6.85	4.276%	$7.1429	$7.14	$7.15	$7.10
Purchase #2	$50.76	3.406%	$52.4889	$52.49	$52.50	$52.50
Purchase #3	$44.71	10.800%	$49.5387	$49.54	$49.55	$49.50
Purchase #4	$92.25	8.390%	$99.9898	$99.99	$100.00	$100.00
Purchase #5	$89.37	5.350%	$94.1513	$94.15	$94.15	$94.20
Purchase #6	$200.89	10.471%	$221.9252	$221.93	$221.95	$221.90
Purchase #7	$89.65	10.642%	$99.1906	$99.19	$99.20	$99.20
7 purchase totals =	$574.48		$624.4274	$624.43	$624.50	$624.40