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	$102.39	9.165%	$111.774	$111.77	$111.75	$111.80
Purchase #2	$157.90	7.286%	$169.4046	$169.40	$169.40	$169.40
Purchase #3	$66.85	9.130%	$72.9534	$72.95	$72.95	$73.00
Purchase #4	$150.96	5.731%	$159.6115	$159.61	$159.60	$159.60
Purchase #5	$161.82	11.462%	$180.3678	$180.37	$180.35	$180.40
Purchase #6	$80.64	8.391%	$87.4065	$87.41	$87.40	$87.40
Purchase #7	$50.92	8.598%	$55.2981	$55.30	$55.30	$55.30
7 purchase totals =	$771.48		$836.8159	$836.81	$836.75	$836.90