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	$132.45	8.419%	$143.601	$143.60	$143.60	$143.60
Purchase #2	$62.73	4.268%	$65.4073	$65.41	$65.40	$65.40
Purchase #3	$120.88	13.477%	$137.171	$137.17	$137.15	$137.20
Purchase #4	$166.36	11.601%	$185.6594	$185.66	$185.65	$185.70
Purchase #5	$159.79	10.158%	$176.0215	$176.02	$176.00	$176.00
Purchase #6	$86.33	9.569%	$94.5909	$94.59	$94.60	$94.60
Purchase #7	$159.32	3.761%	$165.312	$165.31	$165.30	$165.30
7 purchase totals =	$887.86		$967.7631	$967.76	$967.70	$967.80