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	$219.38	12.768%	$247.3904	$247.39	$247.40	$247.40
Purchase #2	$139.41	11.403%	$155.3069	$155.31	$155.30	$155.30
Purchase #3	$231.52	8.171%	$250.4375	$250.44	$250.45	$250.40
Purchase #4	$13.80	5.512%	$14.5607	$14.56	$14.55	$14.60
Purchase #5	$18.29	13.870%	$20.8268	$20.83	$20.85	$20.80
Purchase #6	$235.25	3.413%	$243.2791	$243.28	$243.30	$243.30
Purchase #7	$99.93	4.851%	$104.7776	$104.78	$104.80	$104.80
7 purchase totals =	$957.58		$1,036.5790	$1,036.59	$1,036.65	$1,036.60