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	$79.75	13.407%	$90.4421	$90.44	$90.45	$90.40
Purchase #2	$160.65	7.629%	$172.906	$172.91	$172.90	$172.90
Purchase #3	$65.55	10.513%	$72.4413	$72.44	$72.45	$72.40
Purchase #4	$150.51	10.282%	$165.9854	$165.99	$166.00	$166.00
Purchase #5	$81.67	6.657%	$87.1068	$87.11	$87.10	$87.10
Purchase #6	$67.70	10.627%	$74.8945	$74.89	$74.90	$74.90
Purchase #7	$238.96	8.268%	$258.7172	$258.72	$258.70	$258.70
7 purchase totals =	$844.79		$922.4933	$922.50	$922.50	$922.40