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	$40.88	6.461%	$43.5213	$43.52	$43.50	$43.50
Purchase #2	$101.46	11.428%	$113.0548	$113.05	$113.05	$113.10
Purchase #3	$191.61	9.773%	$210.336	$210.34	$210.35	$210.30
Purchase #4	$61.75	4.794%	$64.7103	$64.71	$64.70	$64.70
Purchase #5	$131.62	11.512%	$146.7721	$146.77	$146.75	$146.80
Purchase #6	$194.40	9.690%	$213.2374	$213.24	$213.25	$213.20
Purchase #7	$173.60	6.556%	$184.9812	$184.98	$185.00	$185.00
7 purchase totals =	$895.32		$976.6131	$976.61	$976.60	$976.60