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	$158.89	7.752%	$171.2072	$171.21	$171.20	$171.20
Purchase #2	$156.25	6.425%	$166.2891	$166.29	$166.30	$166.30
Purchase #3	$108.78	11.640%	$121.442	$121.44	$121.45	$121.40
Purchase #4	$242.78	12.225%	$272.4599	$272.46	$272.45	$272.50
Purchase #5	$50.26	10.654%	$55.6147	$55.61	$55.60	$55.60
Purchase #6	$198.59	5.867%	$210.2413	$210.24	$210.25	$210.20
Purchase #7	$77.49	6.450%	$82.4881	$82.49	$82.50	$82.50
7 purchase totals =	$993.04		$1,079.7423	$1,079.74	$1,079.75	$1,079.70