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	$72.41	11.225%	$80.538	$80.54	$80.55	$80.50
Purchase #2	$240.31	4.790%	$251.8208	$251.82	$251.80	$251.80
Purchase #3	$6.81	12.429%	$7.6564	$7.66	$7.65	$7.70
Purchase #4	$225.67	10.449%	$249.2503	$249.25	$249.25	$249.30
Purchase #5	$9.52	9.272%	$10.4027	$10.40	$10.40	$10.40
Purchase #6	$152.28	13.834%	$173.3464	$173.35	$173.35	$173.30
Purchase #7	$153.48	10.420%	$169.4726	$169.47	$169.45	$169.50
7 purchase totals =	$860.48		$942.4872	$942.49	$942.45	$942.50