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	$70.32	4.349%	$73.3782	$73.38	$73.40	$73.40
Purchase #2	$103.76	11.798%	$116.0016	$116.00	$116.00	$116.00
Purchase #3	$12.30	12.288%	$13.8114	$13.81	$13.80	$13.80
Purchase #4	$249.31	10.418%	$275.2831	$275.28	$275.30	$275.30
Purchase #5	$15.31	4.260%	$15.9622	$15.96	$15.95	$16.00
Purchase #6	$170.56	8.828%	$185.617	$185.62	$185.60	$185.60
Purchase #7	$179.78	6.406%	$191.2967	$191.30	$191.30	$191.30
7 purchase totals =	$801.34		$871.3502	$871.35	$871.35	$871.40