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	$103.87	6.205%	$110.3151	$110.32	$110.30	$110.30
Purchase #2	$84.82	5.410%	$89.4088	$89.41	$89.40	$89.40
Purchase #3	$82.62	5.690%	$87.3211	$87.32	$87.30	$87.30
Purchase #4	$105.84	5.767%	$111.9438	$111.94	$111.95	$111.90
Purchase #5	$31.25	11.568%	$34.865	$34.87	$34.85	$34.90
Purchase #6	$123.88	4.593%	$129.5698	$129.57	$129.55	$129.60
Purchase #7	$94.39	6.729%	$100.7415	$100.74	$100.75	$100.70
7 purchase totals =	$626.67		$664.1651	$664.17	$664.10	$664.10