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	$71.53	9.756%	$78.5085	$78.51	$78.50	$78.50
Purchase #2	$42.45	12.821%	$47.8925	$47.89	$47.90	$47.90
Purchase #3	$115.91	10.360%	$127.9183	$127.92	$127.90	$127.90
Purchase #4	$233.68	4.301%	$243.7306	$243.73	$243.75	$243.70
Purchase #5	$30.61	3.284%	$31.6152	$31.62	$31.60	$31.60
Purchase #6	$21.94	5.136%	$23.0668	$23.07	$23.05	$23.10
Purchase #7	$240.96	12.662%	$271.4704	$271.47	$271.45	$271.50
7 purchase totals =	$757.08		$824.2023	$824.21	$824.15	$824.20