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	$15.77	6.723%	$16.8302	$16.83	$16.85	$16.80
Purchase #2	$244.71	13.417%	$277.5427	$277.54	$277.55	$277.50
Purchase #3	$89.28	10.302%	$98.4776	$98.48	$98.50	$98.50
Purchase #4	$246.89	13.489%	$280.193	$280.19	$280.20	$280.20
Purchase #5	$51.98	13.675%	$59.0883	$59.09	$59.10	$59.10
Purchase #6	$90.65	8.731%	$98.5647	$98.56	$98.55	$98.60
Purchase #7	$149.63	11.500%	$166.8375	$166.84	$166.85	$166.80
7 purchase totals =	$888.91		$997.5340	$997.53	$997.60	$997.50