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	$162.86	9.628%	$178.5402	$178.54	$178.55	$178.50
Purchase #2	$91.97	13.310%	$104.2112	$104.21	$104.20	$104.20
Purchase #3	$155.53	10.502%	$171.8638	$171.86	$171.85	$171.90
Purchase #4	$232.31	10.448%	$256.5817	$256.58	$256.60	$256.60
Purchase #5	$151.96	13.675%	$172.7405	$172.74	$172.75	$172.70
Purchase #6	$19.59	13.163%	$22.1686	$22.17	$22.15	$22.20
Purchase #7	$27.97	13.792%	$31.8276	$31.83	$31.85	$31.80
7 purchase totals =	$842.19		$937.9336	$937.93	$937.95	$937.90