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	$52.97	5.508%	$55.8876	$55.89	$55.90	$55.90
Purchase #2	$110.93	3.842%	$115.1919	$115.19	$115.20	$115.20
Purchase #3	$104.37	12.563%	$117.482	$117.48	$117.50	$117.50
Purchase #4	$79.80	3.351%	$82.4741	$82.47	$82.45	$82.50
Purchase #5	$86.32	3.781%	$89.5838	$89.58	$89.60	$89.60
Purchase #6	$190.62	10.620%	$210.8638	$210.86	$210.85	$210.90
Purchase #7	$50.37	10.537%	$55.6775	$55.68	$55.70	$55.70
7 purchase totals =	$675.38		$727.1607	$727.15	$727.20	$727.30