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	$250.93	5.184%	$263.9382	$263.94	$263.95	$263.90
Purchase #2	$124.82	11.789%	$139.535	$139.54	$139.55	$139.50
Purchase #3	$223.41	12.815%	$252.04	$252.04	$252.05	$252.00
Purchase #4	$121.47	8.325%	$131.5824	$131.58	$131.60	$131.60
Purchase #5	$85.46	7.217%	$91.6276	$91.63	$91.65	$91.60
Purchase #6	$127.32	13.350%	$144.3172	$144.32	$144.30	$144.30
Purchase #7	$33.29	6.268%	$35.3766	$35.38	$35.40	$35.40
7 purchase totals =	$966.70		$1,058.4170	$1,058.43	$1,058.50	$1,058.30