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	$40.36	4.336%	$42.11	$42.11	$42.10	$42.10
Purchase #2	$28.96	11.512%	$32.2939	$32.29	$32.30	$32.30
Purchase #3	$138.55	13.308%	$156.9882	$156.99	$157.00	$157.00
Purchase #4	$154.64	11.553%	$172.5056	$172.51	$172.50	$172.50
Purchase #5	$71.95	6.164%	$76.385	$76.39	$76.40	$76.40
Purchase #6	$238.54	5.507%	$251.6764	$251.68	$251.70	$251.70
Purchase #7	$145.43	13.845%	$165.5648	$165.56	$165.55	$165.60
7 purchase totals =	$818.43		$897.5239	$897.53	$897.55	$897.60