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	$48.89	6.702%	$52.1666	$52.17	$52.15	$52.20
Purchase #2	$131.93	9.485%	$144.4436	$144.44	$144.45	$144.40
Purchase #3	$214.29	9.131%	$233.8568	$233.86	$233.85	$233.90
Purchase #4	$117.65	3.524%	$121.796	$121.80	$121.80	$121.80
Purchase #5	$109.37	12.657%	$123.213	$123.21	$123.20	$123.20
Purchase #6	$74.45	5.459%	$78.5142	$78.51	$78.50	$78.50
Purchase #7	$117.35	7.230%	$125.8344	$125.83	$125.85	$125.80
7 purchase totals =	$813.93		$879.8246	$879.82	$879.80	$879.80