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	$241.58	11.852%	$270.2121	$270.21	$270.20	$270.20
Purchase #2	$124.60	13.606%	$141.5531	$141.55	$141.55	$141.60
Purchase #3	$59.49	12.441%	$66.8912	$66.89	$66.90	$66.90
Purchase #4	$83.87	13.307%	$95.0306	$95.03	$95.05	$95.00
Purchase #5	$53.94	7.139%	$57.7908	$57.79	$57.80	$57.80
Purchase #6	$47.80	10.226%	$52.688	$52.69	$52.70	$52.70
Purchase #7	$243.53	6.236%	$258.7165	$258.72	$258.70	$258.70
7 purchase totals =	$854.81		$942.8823	$942.88	$942.90	$942.90