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	$102.72	9.203%	$112.1733	$112.17	$112.15	$112.20
Purchase #2	$145.36	10.846%	$161.1257	$161.13	$161.15	$161.10
Purchase #3	$235.29	12.255%	$264.1248	$264.12	$264.10	$264.10
Purchase #4	$92.64	7.756%	$99.8252	$99.83	$99.85	$99.80
Purchase #5	$183.56	5.593%	$193.8265	$193.83	$193.85	$193.80
Purchase #6	$241.41	9.293%	$263.8442	$263.84	$263.85	$263.80
Purchase #7	$49.61	11.207%	$55.1698	$55.17	$55.15	$55.20
7 purchase totals =	$1,050.59		$1,150.0895	$1,150.09	$1,150.10	$1,150.00