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	$109.61	7.571%	$117.9086	$117.91	$117.90	$117.90
Purchase #2	$57.82	3.726%	$59.9744	$59.97	$59.95	$60.00
Purchase #3	$216.55	5.712%	$228.9193	$228.92	$228.90	$228.90
Purchase #4	$215.25	7.129%	$230.5952	$230.60	$230.60	$230.60
Purchase #5	$183.62	7.180%	$196.8039	$196.80	$196.80	$196.80
Purchase #6	$133.35	8.501%	$144.6861	$144.69	$144.70	$144.70
Purchase #7	$88.72	11.487%	$98.9113	$98.91	$98.90	$98.90
7 purchase totals =	$1,004.92		$1,077.7988	$1,077.80	$1,077.75	$1,077.80