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	$65.59	10.244%	$72.309	$72.31	$72.30	$72.30
Purchase #2	$138.64	13.601%	$157.4964	$157.50	$157.50	$157.50
Purchase #3	$149.80	8.286%	$162.2124	$162.21	$162.20	$162.20
Purchase #4	$185.95	10.815%	$206.0605	$206.06	$206.05	$206.10
Purchase #5	$157.33	7.733%	$169.4963	$169.50	$169.50	$169.50
Purchase #6	$250.94	7.572%	$269.9412	$269.94	$269.95	$269.90
Purchase #7	$137.88	9.332%	$150.747	$150.75	$150.75	$150.70
7 purchase totals =	$1,086.13		$1,188.2628	$1,188.27	$1,188.25	$1,188.20