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	$37.76	4.109%	$39.3116	$39.31	$39.30	$39.30
Purchase #2	$134.54	3.745%	$139.5785	$139.58	$139.60	$139.60
Purchase #3	$220.57	13.727%	$250.8476	$250.85	$250.85	$250.80
Purchase #4	$229.57	3.854%	$238.4176	$238.42	$238.40	$238.40
Purchase #5	$69.63	4.771%	$72.952	$72.95	$72.95	$73.00
Purchase #6	$223.77	5.122%	$235.2315	$235.23	$235.25	$235.20
Purchase #7	$223.63	13.201%	$253.1514	$253.15	$253.15	$253.20
7 purchase totals =	$1,139.47		$1,229.4902	$1,229.49	$1,229.50	$1,229.50