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	$87.78	3.165%	$90.5582	$90.56	$90.55	$90.60
Purchase #2	$200.33	4.662%	$209.6694	$209.67	$209.65	$209.70
Purchase #3	$227.52	10.677%	$251.8123	$251.81	$251.80	$251.80
Purchase #4	$14.78	5.268%	$15.5586	$15.56	$15.55	$15.60
Purchase #5	$223.87	12.810%	$252.5477	$252.55	$252.55	$252.50
Purchase #6	$42.61	10.653%	$47.1492	$47.15	$47.15	$47.10
Purchase #7	$161.25	13.681%	$183.3106	$183.31	$183.30	$183.30
7 purchase totals =	$958.14		$1,050.6060	$1,050.61	$1,050.55	$1,050.60