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	$89.60	12.427%	$100.7346	$100.73	$100.75	$100.70
Purchase #2	$142.70	10.866%	$158.2058	$158.21	$158.20	$158.20
Purchase #3	$89.58	7.601%	$96.389	$96.39	$96.40	$96.40
Purchase #4	$87.56	4.579%	$91.5694	$91.57	$91.55	$91.60
Purchase #5	$117.27	10.566%	$129.6607	$129.66	$129.65	$129.70
Purchase #6	$157.35	3.245%	$162.456	$162.46	$162.45	$162.50
Purchase #7	$226.36	12.402%	$254.4332	$254.43	$254.45	$254.40
7 purchase totals =	$910.42		$993.4487	$993.45	$993.45	$993.50