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	$72.69	10.600%	$80.3951	$80.40	$80.40	$80.40
Purchase #2	$63.31	5.160%	$66.5768	$66.58	$66.60	$66.60
Purchase #3	$225.40	13.288%	$255.3512	$255.35	$255.35	$255.40
Purchase #4	$250.27	6.799%	$267.2859	$267.29	$267.30	$267.30
Purchase #5	$212.67	10.285%	$234.5431	$234.54	$234.55	$234.50
Purchase #6	$221.91	8.802%	$241.4425	$241.44	$241.45	$241.40
Purchase #7	$19.51	3.459%	$20.1849	$20.18	$20.20	$20.20
7 purchase totals =	$1,065.76		$1,165.7795	$1,165.78	$1,165.85	$1,165.80