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	$122.91	12.633%	$138.4372	$138.44	$138.45	$138.40
Purchase #2	$92.73	7.165%	$99.3741	$99.37	$99.35	$99.40
Purchase #3	$210.43	8.322%	$227.942	$227.94	$227.95	$227.90
Purchase #4	$193.43	3.247%	$199.7107	$199.71	$199.70	$199.70
Purchase #5	$146.87	6.634%	$156.6134	$156.61	$156.60	$156.60
Purchase #6	$59.38	3.729%	$61.5943	$61.59	$61.60	$61.60
Purchase #7	$156.41	7.494%	$168.1314	$168.13	$168.15	$168.10
7 purchase totals =	$982.16		$1,051.8031	$1,051.79	$1,051.80	$1,051.70