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	$84.52	5.324%	$89.0198	$89.02	$89.00	$89.00
Purchase #2	$156.51	11.106%	$173.892	$173.89	$173.90	$173.90
Purchase #3	$60.96	9.468%	$66.7317	$66.73	$66.75	$66.70
Purchase #4	$148.67	11.472%	$165.7254	$165.73	$165.75	$165.70
Purchase #5	$229.42	9.695%	$251.6623	$251.66	$251.65	$251.70
Purchase #6	$109.35	8.208%	$118.3254	$118.33	$118.35	$118.30
Purchase #7	$220.41	6.158%	$233.9828	$233.98	$234.00	$234.00
7 purchase totals =	$1,009.84		$1,099.3394	$1,099.34	$1,099.40	$1,099.30