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	$17.51	6.305%	$18.614	$18.61	$18.60	$18.60
Purchase #2	$212.96	12.116%	$238.7622	$238.76	$238.75	$238.80
Purchase #3	$118.59	5.543%	$125.1634	$125.16	$125.15	$125.20
Purchase #4	$52.47	10.399%	$57.9264	$57.93	$57.95	$57.90
Purchase #5	$59.88	3.774%	$62.1399	$62.14	$62.15	$62.10
Purchase #6	$31.42	7.165%	$33.6712	$33.67	$33.65	$33.70
Purchase #7	$234.63	13.162%	$265.512	$265.51	$265.50	$265.50
7 purchase totals =	$727.46		$801.7891	$801.78	$801.75	$801.80