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	$28.32	11.457%	$31.5646	$31.56	$31.55	$31.60
Purchase #2	$197.94	9.634%	$217.0095	$217.01	$217.00	$217.00
Purchase #3	$231.86	7.325%	$248.8437	$248.84	$248.85	$248.80
Purchase #4	$89.41	11.386%	$99.5902	$99.59	$99.60	$99.60
Purchase #5	$166.63	3.411%	$172.3137	$172.31	$172.30	$172.30
Purchase #6	$214.70	12.824%	$242.2331	$242.23	$242.25	$242.20
Purchase #7	$39.74	9.198%	$43.3953	$43.40	$43.40	$43.40
7 purchase totals =	$968.60		$1,054.9501	$1,054.94	$1,054.95	$1,054.90