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	$43.67	3.708%	$45.2893	$45.29	$45.30	$45.30
Purchase #2	$122.50	11.384%	$136.4454	$136.45	$136.45	$136.40
Purchase #3	$39.58	4.167%	$41.2293	$41.23	$41.25	$41.20
Purchase #4	$104.50	7.566%	$112.4065	$112.41	$112.40	$112.40
Purchase #5	$152.80	5.300%	$160.8984	$160.90	$160.90	$160.90
Purchase #6	$150.49	10.849%	$166.8167	$166.82	$166.80	$166.80
Purchase #7	$45.51	4.864%	$47.7236	$47.72	$47.70	$47.70
7 purchase totals =	$659.05		$710.8092	$710.82	$710.80	$710.70