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	$71.89	8.698%	$78.143	$78.14	$78.15	$78.10
Purchase #2	$92.82	5.213%	$97.6587	$97.66	$97.65	$97.70
Purchase #3	$112.67	13.349%	$127.7103	$127.71	$127.70	$127.70
Purchase #4	$120.49	6.269%	$128.0435	$128.04	$128.05	$128.00
Purchase #5	$81.47	9.366%	$89.1005	$89.10	$89.10	$89.10
Purchase #6	$28.30	11.327%	$31.5055	$31.51	$31.50	$31.50
Purchase #7	$233.57	10.447%	$257.9711	$257.97	$257.95	$258.00
7 purchase totals =	$741.21		$810.1326	$810.13	$810.10	$810.10