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	$238.36	7.231%	$255.5958	$255.60	$255.60	$255.60
Purchase #2	$93.96	11.306%	$104.5831	$104.58	$104.60	$104.60
Purchase #3	$54.35	10.289%	$59.9421	$59.94	$59.95	$59.90
Purchase #4	$245.30	3.315%	$253.4317	$253.43	$253.45	$253.40
Purchase #5	$56.82	6.198%	$60.3417	$60.34	$60.35	$60.30
Purchase #6	$235.83	9.814%	$258.9744	$258.97	$258.95	$259.00
Purchase #7	$68.96	10.437%	$76.1574	$76.16	$76.15	$76.20
7 purchase totals =	$993.58		$1,069.0262	$1,069.02	$1,069.05	$1,069.00