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	$107.73	3.321%	$111.3077	$111.31	$111.30	$111.30
Purchase #2	$82.45	12.210%	$92.5171	$92.52	$92.50	$92.50
Purchase #3	$236.86	11.812%	$264.8379	$264.84	$264.85	$264.80
Purchase #4	$220.79	13.542%	$250.6894	$250.69	$250.70	$250.70
Purchase #5	$152.86	12.551%	$172.0455	$172.05	$172.05	$172.00
Purchase #6	$69.75	11.726%	$77.9289	$77.93	$77.95	$77.90
Purchase #7	$40.30	12.619%	$45.3855	$45.39	$45.40	$45.40
7 purchase totals =	$910.74		$1,014.7120	$1,014.73	$1,014.75	$1,014.60