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	$49.71	6.163%	$52.7736	$52.77	$52.75	$52.80
Purchase #2	$89.90	5.535%	$94.876	$94.88	$94.90	$94.90
Purchase #3	$106.38	12.349%	$119.5169	$119.52	$119.50	$119.50
Purchase #4	$229.94	10.690%	$254.5206	$254.52	$254.50	$254.50
Purchase #5	$20.52	12.750%	$23.1363	$23.14	$23.15	$23.10
Purchase #6	$67.36	6.425%	$71.6879	$71.69	$71.70	$71.70
Purchase #7	$66.41	11.262%	$73.8891	$73.89	$73.90	$73.90
7 purchase totals =	$630.22		$690.4004	$690.41	$690.40	$690.40