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	$220.56	13.296%	$249.8857	$249.89	$249.90	$249.90
Purchase #2	$92.33	11.787%	$103.2129	$103.21	$103.20	$103.20
Purchase #3	$153.75	11.289%	$171.1068	$171.11	$171.10	$171.10
Purchase #4	$18.69	4.842%	$19.595	$19.60	$19.60	$19.60
Purchase #5	$244.42	10.438%	$269.9326	$269.93	$269.95	$269.90
Purchase #6	$183.64	5.865%	$194.4105	$194.41	$194.40	$194.40
Purchase #7	$99.29	5.191%	$104.4441	$104.44	$104.45	$104.40
7 purchase totals =	$1,012.68		$1,112.5876	$1,112.59	$1,112.60	$1,112.50