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	$71.59	3.796%	$74.3076	$74.31	$74.30	$74.30
Purchase #2	$144.86	11.813%	$161.9723	$161.97	$161.95	$162.00
Purchase #3	$121.75	12.448%	$136.9054	$136.91	$136.90	$136.90
Purchase #4	$103.46	7.793%	$111.5226	$111.52	$111.50	$111.50
Purchase #5	$14.35	5.677%	$15.1646	$15.16	$15.15	$15.20
Purchase #6	$83.83	12.865%	$94.6147	$94.61	$94.60	$94.60
Purchase #7	$27.46	3.118%	$28.3162	$28.32	$28.30	$28.30
7 purchase totals =	$567.30		$622.8034	$622.80	$622.70	$622.80