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	$160.78	10.591%	$177.8082	$177.81	$177.80	$177.80
Purchase #2	$63.33	6.634%	$67.5313	$67.53	$67.55	$67.50
Purchase #3	$29.71	10.709%	$32.8916	$32.89	$32.90	$32.90
Purchase #4	$144.85	6.431%	$154.1653	$154.17	$154.15	$154.20
Purchase #5	$86.70	3.235%	$89.5047	$89.50	$89.50	$89.50
Purchase #6	$173.93	7.407%	$186.813	$186.81	$186.80	$186.80
Purchase #7	$31.77	6.327%	$33.7801	$33.78	$33.80	$33.80
7 purchase totals =	$691.07		$742.4942	$742.49	$742.50	$742.50