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	$114.47	11.220%	$127.3135	$127.31	$127.30	$127.30
Purchase #2	$93.34	9.351%	$102.0682	$102.07	$102.05	$102.10
Purchase #3	$174.29	6.668%	$185.9117	$185.91	$185.90	$185.90
Purchase #4	$62.88	5.219%	$66.1617	$66.16	$66.15	$66.20
Purchase #5	$175.99	3.746%	$182.5826	$182.58	$182.60	$182.60
Purchase #6	$131.47	13.142%	$148.7478	$148.75	$148.75	$148.70
Purchase #7	$87.98	12.781%	$99.2247	$99.22	$99.20	$99.20
7 purchase totals =	$840.42		$912.0102	$912.00	$911.95	$912.00