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	$168.25	12.690%	$189.6009	$189.60	$189.60	$189.60
Purchase #2	$99.73	8.823%	$108.5292	$108.53	$108.55	$108.50
Purchase #3	$129.60	6.388%	$137.8788	$137.88	$137.90	$137.90
Purchase #4	$172.71	4.216%	$179.9915	$179.99	$180.00	$180.00
Purchase #5	$168.34	13.172%	$190.5137	$190.51	$190.50	$190.50
Purchase #6	$49.70	13.515%	$56.417	$56.42	$56.40	$56.40
Purchase #7	$92.46	4.858%	$96.9517	$96.95	$96.95	$97.00
7 purchase totals =	$880.79		$959.8828	$959.88	$959.90	$959.90