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	$53.54	6.156%	$56.8359	$56.84	$56.85	$56.80
Purchase #2	$90.25	7.216%	$96.7624	$96.76	$96.75	$96.80
Purchase #3	$49.28	8.305%	$53.3727	$53.37	$53.35	$53.40
Purchase #4	$42.79	6.476%	$45.5611	$45.56	$45.55	$45.60
Purchase #5	$55.51	11.511%	$61.8998	$61.90	$61.90	$61.90
Purchase #6	$11.75	6.350%	$12.4961	$12.50	$12.50	$12.50
Purchase #7	$19.62	5.730%	$20.7442	$20.74	$20.75	$20.70
7 purchase totals =	$322.74		$347.6722	$347.67	$347.65	$347.70