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	$165.25	13.353%	$187.3158	$187.32	$187.30	$187.30
Purchase #2	$79.76	12.655%	$89.8536	$89.85	$89.85	$89.90
Purchase #3	$160.47	12.188%	$180.0281	$180.03	$180.05	$180.00
Purchase #4	$165.26	13.694%	$187.8907	$187.89	$187.90	$187.90
Purchase #5	$52.51	5.376%	$55.3329	$55.33	$55.35	$55.30
Purchase #6	$99.32	6.348%	$105.6248	$105.62	$105.60	$105.60
Purchase #7	$33.25	5.214%	$34.9837	$34.98	$35.00	$35.00
7 purchase totals =	$755.82		$841.0296	$841.02	$841.05	$841.00