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	$155.46	7.172%	$166.6096	$166.61	$166.60	$166.60
Purchase #2	$224.83	7.129%	$240.8581	$240.86	$240.85	$240.90
Purchase #3	$245.57	4.477%	$256.5642	$256.56	$256.55	$256.60
Purchase #4	$184.39	10.231%	$203.2549	$203.25	$203.25	$203.30
Purchase #5	$232.46	11.383%	$258.9209	$258.92	$258.90	$258.90
Purchase #6	$63.77	10.513%	$70.4741	$70.47	$70.45	$70.50
Purchase #7	$59.62	6.505%	$63.4983	$63.50	$63.50	$63.50
7 purchase totals =	$1,166.10		$1,260.1801	$1,260.17	$1,260.10	$1,260.30