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	$168.51	13.640%	$191.4948	$191.49	$191.50	$191.50
Purchase #2	$244.85	13.355%	$277.5497	$277.55	$277.55	$277.50
Purchase #3	$102.52	11.518%	$114.3283	$114.33	$114.35	$114.30
Purchase #4	$180.57	11.123%	$200.6548	$200.65	$200.65	$200.70
Purchase #5	$67.33	5.114%	$70.7733	$70.77	$70.75	$70.80
Purchase #6	$27.85	7.285%	$29.8789	$29.88	$29.90	$29.90
Purchase #7	$118.68	12.218%	$133.1803	$133.18	$133.20	$133.20
7 purchase totals =	$910.31		$1,017.8601	$1,017.85	$1,017.90	$1,017.90