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	$16.38	10.611%	$18.1181	$18.12	$18.10	$18.10
Purchase #2	$227.59	12.871%	$256.8831	$256.88	$256.90	$256.90
Purchase #3	$19.30	5.749%	$20.4096	$20.41	$20.40	$20.40
Purchase #4	$43.76	5.218%	$46.0434	$46.04	$46.05	$46.00
Purchase #5	$64.68	10.519%	$71.4837	$71.48	$71.50	$71.50
Purchase #6	$16.91	8.810%	$18.3998	$18.40	$18.40	$18.40
Purchase #7	$23.73	11.769%	$26.5228	$26.52	$26.50	$26.50
7 purchase totals =	$412.35		$457.8605	$457.85	$457.85	$457.80