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	$124.50	5.535%	$131.3911	$131.39	$131.40	$131.40
Purchase #2	$153.50	12.165%	$172.1733	$172.17	$172.15	$172.20
Purchase #3	$104.49	7.721%	$112.5577	$112.56	$112.55	$112.60
Purchase #4	$41.87	5.332%	$44.1025	$44.10	$44.10	$44.10
Purchase #5	$59.81	12.425%	$67.2414	$67.24	$67.25	$67.20
Purchase #6	$216.57	9.652%	$237.4733	$237.47	$237.45	$237.50
Purchase #7	$144.77	10.474%	$159.9332	$159.93	$159.95	$159.90
7 purchase totals =	$845.51		$924.8725	$924.86	$924.85	$924.90