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	$135.32	3.845%	$140.5231	$140.52	$140.50	$140.50
Purchase #2	$124.77	12.710%	$140.6283	$140.63	$140.65	$140.60
Purchase #3	$198.53	4.528%	$207.5194	$207.52	$207.50	$207.50
Purchase #4	$67.29	4.770%	$70.4997	$70.50	$70.50	$70.50
Purchase #5	$179.61	5.199%	$188.9479	$188.95	$188.95	$188.90
Purchase #6	$117.32	9.809%	$128.8279	$128.83	$128.85	$128.80
Purchase #7	$152.68	13.197%	$172.8292	$172.83	$172.85	$172.80
7 purchase totals =	$975.52		$1,049.7755	$1,049.78	$1,049.80	$1,049.60