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	$246.77	4.726%	$258.4324	$258.43	$258.45	$258.40
Purchase #2	$149.61	7.515%	$160.8532	$160.85	$160.85	$160.90
Purchase #3	$7.55	10.379%	$8.3336	$8.33	$8.35	$8.30
Purchase #4	$151.82	4.232%	$158.245	$158.25	$158.25	$158.20
Purchase #5	$222.66	10.675%	$246.429	$246.43	$246.45	$246.40
Purchase #6	$74.91	11.459%	$83.4939	$83.49	$83.50	$83.50
Purchase #7	$84.75	5.269%	$89.2155	$89.22	$89.20	$89.20
7 purchase totals =	$938.07		$1,005.0026	$1,005.00	$1,005.05	$1,004.90