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	$164.54	13.399%	$186.5867	$186.59	$186.60	$186.60
Purchase #2	$119.70	11.598%	$133.5828	$133.58	$133.60	$133.60
Purchase #3	$246.89	13.260%	$279.6276	$279.63	$279.65	$279.60
Purchase #4	$69.57	10.188%	$76.6578	$76.66	$76.65	$76.70
Purchase #5	$70.48	11.637%	$78.6818	$78.68	$78.70	$78.70
Purchase #6	$121.56	10.133%	$133.8777	$133.88	$133.90	$133.90
Purchase #7	$166.77	3.207%	$172.1183	$172.12	$172.10	$172.10
7 purchase totals =	$959.51		$1,061.1327	$1,061.14	$1,061.20	$1,061.20