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	$92.90	11.787%	$103.8501	$103.85	$103.85	$103.90
Purchase #2	$159.27	12.527%	$179.2218	$179.22	$179.20	$179.20
Purchase #3	$130.28	7.149%	$139.5937	$139.59	$139.60	$139.60
Purchase #4	$227.81	5.431%	$240.1824	$240.18	$240.20	$240.20
Purchase #5	$123.25	10.411%	$136.0816	$136.08	$136.10	$136.10
Purchase #6	$174.69	10.166%	$192.449	$192.45	$192.45	$192.40
Purchase #7	$11.37	7.318%	$12.2021	$12.20	$12.20	$12.20
7 purchase totals =	$919.57		$1,003.5807	$1,003.57	$1,003.60	$1,003.60