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	$115.92	6.868%	$123.8814	$123.88	$123.90	$123.90
Purchase #2	$214.40	7.192%	$229.8196	$229.82	$229.80	$229.80
Purchase #3	$249.28	11.852%	$278.8247	$278.82	$278.80	$278.80
Purchase #4	$95.49	8.627%	$103.7279	$103.73	$103.75	$103.70
Purchase #5	$126.31	10.424%	$139.4766	$139.48	$139.50	$139.50
Purchase #6	$116.83	11.561%	$130.3367	$130.34	$130.35	$130.30
Purchase #7	$193.42	13.656%	$219.8334	$219.83	$219.85	$219.80
7 purchase totals =	$1,111.65		$1,225.9003	$1,225.90	$1,225.95	$1,225.80