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	$142.53	13.301%	$161.4879	$161.49	$161.50	$161.50
Purchase #2	$87.72	10.764%	$97.1622	$97.16	$97.15	$97.20
Purchase #3	$188.49	10.588%	$208.4473	$208.45	$208.45	$208.40
Purchase #4	$97.83	9.301%	$106.9292	$106.93	$106.95	$106.90
Purchase #5	$40.90	4.732%	$42.8354	$42.84	$42.85	$42.80
Purchase #6	$231.79	9.324%	$253.4021	$253.40	$253.40	$253.40
Purchase #7	$101.27	10.134%	$111.5327	$111.53	$111.55	$111.50
7 purchase totals =	$890.53		$981.7968	$981.80	$981.85	$981.70