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	$180.50	8.589%	$196.0031	$196.00	$196.00	$196.00
Purchase #2	$107.41	3.530%	$111.2016	$111.20	$111.20	$111.20
Purchase #3	$80.28	12.830%	$90.5799	$90.58	$90.60	$90.60
Purchase #4	$32.34	3.294%	$33.4053	$33.41	$33.40	$33.40
Purchase #5	$195.96	3.612%	$203.0381	$203.04	$203.05	$203.00
Purchase #6	$235.41	12.534%	$264.9163	$264.92	$264.90	$264.90
Purchase #7	$68.37	4.395%	$71.3749	$71.37	$71.35	$71.40
7 purchase totals =	$900.27		$970.5192	$970.52	$970.50	$970.50