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	$149.31	4.229%	$155.6243	$155.62	$155.60	$155.60
Purchase #2	$55.52	13.711%	$63.1323	$63.13	$63.15	$63.10
Purchase #3	$139.44	5.863%	$147.6154	$147.62	$147.60	$147.60
Purchase #4	$237.28	5.529%	$250.3992	$250.40	$250.40	$250.40
Purchase #5	$61.32	10.211%	$67.5814	$67.58	$67.60	$67.60
Purchase #6	$16.31	11.827%	$18.239	$18.24	$18.25	$18.20
Purchase #7	$95.71	10.669%	$105.9213	$105.92	$105.90	$105.90
7 purchase totals =	$754.89		$808.5129	$808.51	$808.50	$808.40