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	$175.92	3.290%	$181.7078	$181.71	$181.70	$181.70
Purchase #2	$108.33	7.184%	$116.1124	$116.11	$116.10	$116.10
Purchase #3	$103.93	7.603%	$111.8318	$111.83	$111.85	$111.80
Purchase #4	$171.51	8.732%	$186.4863	$186.49	$186.50	$186.50
Purchase #5	$45.85	3.581%	$47.4919	$47.49	$47.50	$47.50
Purchase #6	$186.56	13.312%	$211.3949	$211.39	$211.40	$211.40
Purchase #7	$91.55	5.147%	$96.2621	$96.26	$96.25	$96.30
7 purchase totals =	$883.65		$951.2872	$951.28	$951.30	$951.30