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	$160.90	7.262%	$172.5846	$172.58	$172.60	$172.60
Purchase #2	$28.74	12.238%	$32.2572	$32.26	$32.25	$32.30
Purchase #3	$155.82	10.829%	$172.6937	$172.69	$172.70	$172.70
Purchase #4	$157.48	7.247%	$168.8926	$168.89	$168.90	$168.90
Purchase #5	$205.65	7.445%	$220.9606	$220.96	$220.95	$221.00
Purchase #6	$56.49	6.710%	$60.2805	$60.28	$60.30	$60.30
Purchase #7	$79.83	7.372%	$85.7151	$85.72	$85.70	$85.70
7 purchase totals =	$844.91		$913.3843	$913.38	$913.40	$913.50