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	$249.55	10.246%	$275.1189	$275.12	$275.10	$275.10
Purchase #2	$210.99	8.797%	$229.5508	$229.55	$229.55	$229.60
Purchase #3	$42.28	5.484%	$44.5986	$44.60	$44.60	$44.60
Purchase #4	$108.85	6.127%	$115.5192	$115.52	$115.50	$115.50
Purchase #5	$129.34	5.597%	$136.5792	$136.58	$136.60	$136.60
Purchase #6	$35.93	12.537%	$40.4345	$40.43	$40.45	$40.40
Purchase #7	$67.79	7.363%	$72.7814	$72.78	$72.80	$72.80
7 purchase totals =	$844.73		$914.5826	$914.58	$914.60	$914.60