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	$249.41	8.379%	$270.3081	$270.31	$270.30	$270.30
Purchase #2	$50.76	3.602%	$52.5884	$52.59	$52.60	$52.60
Purchase #3	$82.65	7.430%	$88.7909	$88.79	$88.80	$88.80
Purchase #4	$34.99	6.754%	$37.3532	$37.35	$37.35	$37.40
Purchase #5	$72.79	8.423%	$78.9211	$78.92	$78.90	$78.90
Purchase #6	$108.94	4.527%	$113.8717	$113.87	$113.85	$113.90
Purchase #7	$198.86	6.662%	$212.1081	$212.11	$212.10	$212.10
7 purchase totals =	$798.40		$853.9415	$853.94	$853.90	$854.00