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	$244.53	6.123%	$259.5026	$259.50	$259.50	$259.50
Purchase #2	$142.39	7.809%	$153.5092	$153.51	$153.50	$153.50
Purchase #3	$59.95	13.177%	$67.8496	$67.85	$67.85	$67.80
Purchase #4	$192.91	12.518%	$217.0585	$217.06	$217.05	$217.10
Purchase #5	$37.67	13.250%	$42.6613	$42.66	$42.65	$42.70
Purchase #6	$159.40	13.343%	$180.6687	$180.67	$180.65	$180.70
Purchase #7	$204.60	6.489%	$217.8765	$217.88	$217.90	$217.90
7 purchase totals =	$1,041.45		$1,139.1264	$1,139.13	$1,139.10	$1,139.20