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	$178.37	11.782%	$199.3856	$199.39	$199.40	$199.40
Purchase #2	$242.83	3.224%	$250.6588	$250.66	$250.65	$250.70
Purchase #3	$188.80	12.188%	$211.8109	$211.81	$211.80	$211.80
Purchase #4	$99.36	9.832%	$109.1291	$109.13	$109.15	$109.10
Purchase #5	$147.29	12.225%	$165.2962	$165.30	$165.30	$165.30
Purchase #6	$234.43	7.874%	$252.889	$252.89	$252.90	$252.90
Purchase #7	$41.69	5.274%	$43.8887	$43.89	$43.90	$43.90
7 purchase totals =	$1,132.77		$1,233.0583	$1,233.07	$1,233.10	$1,233.10