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	$90.42	12.280%	$101.5236	$101.52	$101.50	$101.50
Purchase #2	$141.88	13.200%	$160.6082	$160.61	$160.60	$160.60
Purchase #3	$207.81	8.422%	$225.3118	$225.31	$225.30	$225.30
Purchase #4	$168.83	3.288%	$174.3811	$174.38	$174.40	$174.40
Purchase #5	$26.47	4.256%	$27.5966	$27.60	$27.60	$27.60
Purchase #6	$110.80	6.377%	$117.8657	$117.87	$117.85	$117.90
Purchase #7	$173.88	6.801%	$185.7056	$185.71	$185.70	$185.70
7 purchase totals =	$920.09		$992.9926	$993.00	$992.95	$993.00