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	$74.36	5.467%	$78.4253	$78.43	$78.45	$78.40
Purchase #2	$149.47	11.872%	$167.2151	$167.22	$167.20	$167.20
Purchase #3	$33.37	12.387%	$37.5035	$37.50	$37.50	$37.50
Purchase #4	$147.87	9.753%	$162.2918	$162.29	$162.30	$162.30
Purchase #5	$133.52	4.636%	$139.71	$139.71	$139.70	$139.70
Purchase #6	$71.61	13.418%	$81.2186	$81.22	$81.20	$81.20
Purchase #7	$29.68	8.567%	$32.2227	$32.22	$32.20	$32.20
7 purchase totals =	$639.88		$698.5870	$698.59	$698.55	$698.50