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	$62.66	8.170%	$67.7793	$67.78	$67.80	$67.80
Purchase #2	$61.38	6.738%	$65.5158	$65.52	$65.50	$65.50
Purchase #3	$244.55	6.268%	$259.8784	$259.88	$259.90	$259.90
Purchase #4	$220.87	6.322%	$234.8334	$234.83	$234.85	$234.80
Purchase #5	$6.65	11.715%	$7.429	$7.43	$7.45	$7.40
Purchase #6	$138.53	9.445%	$151.6142	$151.61	$151.60	$151.60
Purchase #7	$156.50	9.341%	$171.1187	$171.12	$171.10	$171.10
7 purchase totals =	$891.14		$958.1688	$958.17	$958.20	$958.10