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	$82.31	10.393%	$90.8645	$90.86	$90.85	$90.90
Purchase #2	$144.54	4.232%	$150.6569	$150.66	$150.65	$150.70
Purchase #3	$219.58	8.144%	$237.4626	$237.46	$237.45	$237.50
Purchase #4	$104.51	12.587%	$117.6647	$117.66	$117.65	$117.70
Purchase #5	$93.71	7.745%	$100.9678	$100.97	$100.95	$101.00
Purchase #6	$230.60	3.847%	$239.4712	$239.47	$239.45	$239.50
Purchase #7	$61.54	7.702%	$66.2798	$66.28	$66.30	$66.30
7 purchase totals =	$936.79		$1,003.3675	$1,003.36	$1,003.30	$1,003.60