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	$102.94	8.669%	$111.8639	$111.86	$111.85	$111.90
Purchase #2	$56.71	3.664%	$58.7879	$58.79	$58.80	$58.80
Purchase #3	$160.86	3.377%	$166.2922	$166.29	$166.30	$166.30
Purchase #4	$154.28	7.451%	$165.7754	$165.78	$165.80	$165.80
Purchase #5	$145.50	3.271%	$150.2593	$150.26	$150.25	$150.30
Purchase #6	$72.59	8.697%	$78.9032	$78.90	$78.90	$78.90
Purchase #7	$127.66	4.425%	$133.309	$133.31	$133.30	$133.30
7 purchase totals =	$820.54		$865.1909	$865.19	$865.20	$865.30