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	$35.32	11.234%	$39.2878	$39.29	$39.30	$39.30
Purchase #2	$118.35	10.257%	$130.4892	$130.49	$130.50	$130.50
Purchase #3	$104.33	11.223%	$116.039	$116.04	$116.05	$116.00
Purchase #4	$97.85	5.348%	$103.083	$103.08	$103.10	$103.10
Purchase #5	$222.81	12.470%	$250.5944	$250.59	$250.60	$250.60
Purchase #6	$237.57	4.130%	$247.3816	$247.38	$247.40	$247.40
Purchase #7	$90.72	7.529%	$97.5503	$97.55	$97.55	$97.60
7 purchase totals =	$906.95		$984.4253	$984.42	$984.50	$984.50