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	$131.67	3.739%	$136.5931	$136.59	$136.60	$136.60
Purchase #2	$240.63	6.651%	$256.6343	$256.63	$256.65	$256.60
Purchase #3	$151.96	6.778%	$162.2598	$162.26	$162.25	$162.30
Purchase #4	$34.99	7.425%	$37.588	$37.59	$37.60	$37.60
Purchase #5	$227.66	11.328%	$253.4493	$253.45	$253.45	$253.40
Purchase #6	$101.44	10.143%	$111.7291	$111.73	$111.75	$111.70
Purchase #7	$130.59	12.608%	$147.0548	$147.05	$147.05	$147.10
7 purchase totals =	$1,018.94		$1,105.3084	$1,105.30	$1,105.35	$1,105.30