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	$150.45	13.651%	$170.9879	$170.99	$171.00	$171.00
Purchase #2	$142.28	11.589%	$158.7688	$158.77	$158.75	$158.80
Purchase #3	$52.88	4.163%	$55.0814	$55.08	$55.10	$55.10
Purchase #4	$199.94	7.441%	$214.8175	$214.82	$214.80	$214.80
Purchase #5	$204.27	6.735%	$218.0276	$218.03	$218.05	$218.00
Purchase #6	$19.96	6.809%	$21.3191	$21.32	$21.30	$21.30
Purchase #7	$209.32	6.257%	$222.4172	$222.42	$222.40	$222.40
7 purchase totals =	$979.10		$1,061.4195	$1,061.43	$1,061.40	$1,061.40