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	$25.88	9.605%	$28.3658	$28.37	$28.35	$28.40
Purchase #2	$29.88	12.438%	$33.5965	$33.60	$33.60	$33.60
Purchase #3	$36.43	12.185%	$40.869	$40.87	$40.85	$40.90
Purchase #4	$59.55	13.841%	$67.7923	$67.79	$67.80	$67.80
Purchase #5	$156.37	8.367%	$169.4535	$169.45	$169.45	$169.50
Purchase #6	$159.72	12.741%	$180.0699	$180.07	$180.05	$180.10
Purchase #7	$87.73	11.648%	$97.9488	$97.95	$97.95	$97.90
7 purchase totals =	$555.56		$618.0958	$618.10	$618.05	$618.20