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	$10.84	11.468%	$12.0831	$12.08	$12.10	$12.10
Purchase #2	$166.39	7.589%	$179.0173	$179.02	$179.00	$179.00
Purchase #3	$89.28	8.421%	$96.7983	$96.80	$96.80	$96.80
Purchase #4	$47.31	6.399%	$50.3374	$50.34	$50.35	$50.30
Purchase #5	$53.99	9.456%	$59.0953	$59.10	$59.10	$59.10
Purchase #6	$69.84	4.313%	$72.8522	$72.85	$72.85	$72.90
Purchase #7	$172.64	6.776%	$184.3381	$184.34	$184.35	$184.30
7 purchase totals =	$610.29		$654.5217	$654.53	$654.55	$654.50