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	$62.79	6.535%	$66.8933	$66.89	$66.90	$66.90
Purchase #2	$31.84	4.588%	$33.3008	$33.30	$33.30	$33.30
Purchase #3	$152.73	13.340%	$173.1042	$173.10	$173.10	$173.10
Purchase #4	$97.31	12.262%	$109.2422	$109.24	$109.25	$109.20
Purchase #5	$37.87	12.298%	$42.5273	$42.53	$42.55	$42.50
Purchase #6	$243.70	5.283%	$256.5747	$256.57	$256.55	$256.60
Purchase #7	$52.87	11.582%	$58.9934	$58.99	$59.00	$59.00
7 purchase totals =	$679.11		$740.6359	$740.62	$740.65	$740.60