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	$45.76	11.497%	$51.021	$51.02	$51.00	$51.00
Purchase #2	$102.66	13.411%	$116.4277	$116.43	$116.45	$116.40
Purchase #3	$98.99	4.120%	$103.0684	$103.07	$103.05	$103.10
Purchase #4	$99.99	4.470%	$104.4596	$104.46	$104.45	$104.50
Purchase #5	$155.73	6.696%	$166.1577	$166.16	$166.15	$166.20
Purchase #6	$180.91	13.609%	$205.53	$205.53	$205.55	$205.50
Purchase #7	$16.85	7.344%	$18.0875	$18.09	$18.10	$18.10
7 purchase totals =	$700.89		$764.7519	$764.76	$764.75	$764.80