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	$171.53	9.226%	$187.3554	$187.36	$187.35	$187.40
Purchase #2	$241.27	7.636%	$259.6934	$259.69	$259.70	$259.70
Purchase #3	$135.89	3.425%	$140.5442	$140.54	$140.55	$140.50
Purchase #4	$76.70	7.130%	$82.1687	$82.17	$82.15	$82.20
Purchase #5	$72.37	10.720%	$80.1281	$80.13	$80.15	$80.10
Purchase #6	$228.34	7.650%	$245.808	$245.81	$245.80	$245.80
Purchase #7	$57.70	13.723%	$65.6182	$65.62	$65.60	$65.60
7 purchase totals =	$983.80		$1,061.3160	$1,061.32	$1,061.30	$1,061.30