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	$192.99	3.710%	$200.1499	$200.15	$200.15	$200.10
Purchase #2	$191.92	6.260%	$203.9342	$203.93	$203.95	$203.90
Purchase #3	$144.66	10.240%	$159.4732	$159.47	$159.45	$159.50
Purchase #4	$24.81	12.482%	$27.9068	$27.91	$27.90	$27.90
Purchase #5	$27.77	13.647%	$31.5598	$31.56	$31.55	$31.60
Purchase #6	$216.55	6.859%	$231.4032	$231.40	$231.40	$231.40
Purchase #7	$38.54	4.575%	$40.3032	$40.30	$40.30	$40.30
7 purchase totals =	$837.24		$894.7303	$894.72	$894.70	$894.70