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	$225.59	8.108%	$243.8808	$243.88	$243.90	$243.90
Purchase #2	$183.44	9.204%	$200.3238	$200.32	$200.30	$200.30
Purchase #3	$117.94	3.763%	$122.3781	$122.38	$122.40	$122.40
Purchase #4	$70.61	3.846%	$73.3257	$73.33	$73.35	$73.30
Purchase #5	$63.72	5.590%	$67.2819	$67.28	$67.30	$67.30
Purchase #6	$128.35	10.406%	$141.7061	$141.71	$141.70	$141.70
Purchase #7	$160.42	7.583%	$172.5846	$172.58	$172.60	$172.60
7 purchase totals =	$950.07		$1,021.4810	$1,021.48	$1,021.55	$1,021.50