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	$142.57	11.383%	$158.7987	$158.80	$158.80	$158.80
Purchase #2	$55.42	7.871%	$59.7821	$59.78	$59.80	$59.80
Purchase #3	$29.37	12.854%	$33.1452	$33.15	$33.15	$33.10
Purchase #4	$89.97	9.792%	$98.7799	$98.78	$98.80	$98.80
Purchase #5	$137.39	13.203%	$155.5296	$155.53	$155.55	$155.50
Purchase #6	$153.46	11.334%	$170.8532	$170.85	$170.85	$170.90
Purchase #7	$156.87	13.773%	$178.4757	$178.48	$178.50	$178.50
7 purchase totals =	$765.05		$855.3644	$855.37	$855.45	$855.40