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	$240.70	7.855%	$259.607	$259.61	$259.60	$259.60
Purchase #2	$102.92	7.725%	$110.8706	$110.87	$110.85	$110.90
Purchase #3	$57.55	3.867%	$59.7755	$59.78	$59.80	$59.80
Purchase #4	$7.86	9.399%	$8.5988	$8.60	$8.60	$8.60
Purchase #5	$111.45	8.221%	$120.6123	$120.61	$120.60	$120.60
Purchase #6	$74.72	12.238%	$83.8642	$83.86	$83.85	$83.90
Purchase #7	$138.25	3.210%	$142.6878	$142.69	$142.70	$142.70
7 purchase totals =	$733.45		$786.0162	$786.02	$786.00	$786.10