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	$17.45	7.274%	$18.7193	$18.72	$18.70	$18.70
Purchase #2	$31.92	11.486%	$35.5863	$35.59	$35.60	$35.60
Purchase #3	$215.41	9.602%	$236.0937	$236.09	$236.10	$236.10
Purchase #4	$88.90	12.768%	$100.2508	$100.25	$100.25	$100.30
Purchase #5	$40.29	4.635%	$42.1574	$42.16	$42.15	$42.20
Purchase #6	$68.44	4.225%	$71.3316	$71.33	$71.35	$71.30
Purchase #7	$124.38	5.365%	$131.053	$131.05	$131.05	$131.10
7 purchase totals =	$586.79		$635.1921	$635.19	$635.20	$635.30