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	$137.28	5.103%	$144.2854	$144.29	$144.30	$144.30
Purchase #2	$185.49	3.632%	$192.227	$192.23	$192.25	$192.20
Purchase #3	$200.40	4.838%	$210.0954	$210.10	$210.10	$210.10
Purchase #4	$107.64	6.782%	$114.9401	$114.94	$114.95	$114.90
Purchase #5	$157.47	9.754%	$172.8296	$172.83	$172.85	$172.80
Purchase #6	$82.56	8.453%	$89.5388	$89.54	$89.55	$89.50
Purchase #7	$188.93	10.808%	$209.3496	$209.35	$209.35	$209.30
7 purchase totals =	$1,059.77		$1,133.2659	$1,133.28	$1,133.35	$1,133.10