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	$19.58	4.800%	$20.5198	$20.52	$20.50	$20.50
Purchase #2	$25.66	9.728%	$28.1562	$28.16	$28.15	$28.20
Purchase #3	$80.34	13.261%	$90.9939	$90.99	$91.00	$91.00
Purchase #4	$46.86	13.294%	$53.0896	$53.09	$53.10	$53.10
Purchase #5	$100.44	11.134%	$111.623	$111.62	$111.60	$111.60
Purchase #6	$59.67	3.336%	$61.6606	$61.66	$61.65	$61.70
Purchase #7	$225.49	7.129%	$241.5652	$241.57	$241.55	$241.60
7 purchase totals =	$558.04		$607.6083	$607.61	$607.55	$607.70