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	$97.32	8.811%	$105.8949	$105.89	$105.90	$105.90
Purchase #2	$167.90	3.131%	$173.1569	$173.16	$173.15	$173.20
Purchase #3	$57.51	12.765%	$64.8512	$64.85	$64.85	$64.90
Purchase #4	$7.79	10.613%	$8.6168	$8.62	$8.60	$8.60
Purchase #5	$189.91	7.556%	$204.2596	$204.26	$204.25	$204.30
Purchase #6	$79.28	4.105%	$82.5344	$82.53	$82.55	$82.50
Purchase #7	$83.74	6.872%	$89.4946	$89.49	$89.50	$89.50
7 purchase totals =	$683.45		$728.8084	$728.80	$728.80	$728.90