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	$128.55	6.686%	$137.1449	$137.14	$137.15	$137.10
Purchase #2	$125.93	12.408%	$141.5554	$141.56	$141.55	$141.60
Purchase #3	$118.62	3.768%	$123.0896	$123.09	$123.10	$123.10
Purchase #4	$216.48	8.223%	$234.2812	$234.28	$234.30	$234.30
Purchase #5	$28.45	13.814%	$32.3801	$32.38	$32.40	$32.40
Purchase #6	$81.43	13.711%	$92.5949	$92.59	$92.60	$92.60
Purchase #7	$122.82	11.458%	$136.8927	$136.89	$136.90	$136.90
7 purchase totals =	$822.28		$897.9388	$897.93	$898.00	$898.00