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	$245.78	9.144%	$268.2541	$268.25	$268.25	$268.30
Purchase #2	$89.29	3.697%	$92.5911	$92.59	$92.60	$92.60
Purchase #3	$232.86	8.348%	$252.2992	$252.30	$252.30	$252.30
Purchase #4	$168.71	12.871%	$190.4247	$190.42	$190.40	$190.40
Purchase #5	$168.52	12.229%	$189.1283	$189.13	$189.15	$189.10
Purchase #6	$29.61	12.246%	$33.236	$33.24	$33.25	$33.20
Purchase #7	$31.80	6.476%	$33.8594	$33.86	$33.85	$33.90
7 purchase totals =	$966.57		$1,059.7928	$1,059.79	$1,059.80	$1,059.80