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	$80.63	11.267%	$89.7146	$89.71	$89.70	$89.70
Purchase #2	$86.83	10.456%	$95.9089	$95.91	$95.90	$95.90
Purchase #3	$32.91	7.836%	$35.4888	$35.49	$35.50	$35.50
Purchase #4	$95.83	6.242%	$101.8117	$101.81	$101.80	$101.80
Purchase #5	$149.66	12.426%	$168.2568	$168.26	$168.25	$168.30
Purchase #6	$178.92	7.525%	$192.3837	$192.38	$192.40	$192.40
Purchase #7	$201.52	7.206%	$216.0415	$216.04	$216.05	$216.00
7 purchase totals =	$826.30		$899.6060	$899.60	$899.60	$899.60