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	$204.45	13.287%	$231.6153	$231.62	$231.60	$231.60
Purchase #2	$74.57	10.208%	$82.1821	$82.18	$82.20	$82.20
Purchase #3	$136.62	10.256%	$150.6317	$150.63	$150.65	$150.60
Purchase #4	$44.85	13.479%	$50.8953	$50.90	$50.90	$50.90
Purchase #5	$226.52	10.526%	$250.3635	$250.36	$250.35	$250.40
Purchase #6	$59.81	3.559%	$61.9386	$61.94	$61.95	$61.90
Purchase #7	$235.40	3.375%	$243.3448	$243.34	$243.35	$243.30
7 purchase totals =	$982.22		$1,070.9713	$1,070.97	$1,071.00	$1,070.90