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	$20.62	11.511%	$22.9936	$22.99	$23.00	$23.00
Purchase #2	$28.35	9.534%	$31.0529	$31.05	$31.05	$31.10
Purchase #3	$32.99	7.475%	$35.456	$35.46	$35.45	$35.50
Purchase #4	$64.71	8.470%	$70.1909	$70.19	$70.20	$70.20
Purchase #5	$203.52	9.300%	$222.4474	$222.45	$222.45	$222.40
Purchase #6	$17.30	8.753%	$18.8143	$18.81	$18.80	$18.80
Purchase #7	$117.34	12.425%	$131.9195	$131.92	$131.90	$131.90
7 purchase totals =	$484.83		$532.8746	$532.87	$532.85	$532.90