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	$163.99	5.329%	$172.729	$172.73	$172.75	$172.70
Purchase #2	$181.66	4.650%	$190.1072	$190.11	$190.10	$190.10
Purchase #3	$135.80	11.435%	$151.3287	$151.33	$151.35	$151.30
Purchase #4	$87.55	13.294%	$99.1889	$99.19	$99.20	$99.20
Purchase #5	$153.40	7.108%	$164.3037	$164.30	$164.30	$164.30
Purchase #6	$28.97	9.162%	$31.6242	$31.62	$31.60	$31.60
Purchase #7	$150.84	13.748%	$171.5775	$171.58	$171.60	$171.60
7 purchase totals =	$902.21		$980.8592	$980.86	$980.90	$980.80