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	$247.85	9.794%	$272.1244	$272.12	$272.10	$272.10
Purchase #2	$154.30	11.267%	$171.685	$171.69	$171.70	$171.70
Purchase #3	$68.47	12.686%	$77.1561	$77.16	$77.15	$77.20
Purchase #4	$70.86	5.166%	$74.5206	$74.52	$74.50	$74.50
Purchase #5	$92.91	5.406%	$97.9327	$97.93	$97.95	$97.90
Purchase #6	$248.72	10.259%	$274.2362	$274.24	$274.25	$274.20
Purchase #7	$208.79	11.679%	$233.1746	$233.17	$233.15	$233.20
7 purchase totals =	$1,091.90		$1,200.8296	$1,200.83	$1,200.80	$1,200.80