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	$135.58	10.821%	$150.2511	$150.25	$150.25	$150.30
Purchase #2	$104.71	12.840%	$118.1548	$118.15	$118.15	$118.20
Purchase #3	$79.38	12.129%	$89.008	$89.01	$89.00	$89.00
Purchase #4	$145.92	11.482%	$162.6745	$162.67	$162.65	$162.70
Purchase #5	$145.84	10.224%	$160.7507	$160.75	$160.75	$160.80
Purchase #6	$211.49	12.678%	$238.3027	$238.30	$238.30	$238.30
Purchase #7	$44.94	7.229%	$48.1887	$48.19	$48.20	$48.20
7 purchase totals =	$867.86		$967.3305	$967.32	$967.30	$967.50