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	$138.69	8.401%	$150.3413	$150.34	$150.35	$150.30
Purchase #2	$194.77	13.676%	$221.4067	$221.41	$221.40	$221.40
Purchase #3	$216.80	4.834%	$227.2801	$227.28	$227.30	$227.30
Purchase #4	$145.75	4.152%	$151.8015	$151.80	$151.80	$151.80
Purchase #5	$172.48	10.351%	$190.3334	$190.33	$190.35	$190.30
Purchase #6	$181.54	9.593%	$198.9551	$198.96	$198.95	$199.00
Purchase #7	$134.95	3.116%	$139.155	$139.16	$139.15	$139.20
7 purchase totals =	$1,184.98		$1,279.2731	$1,279.28	$1,279.30	$1,279.30