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	$89.51	12.251%	$100.4759	$100.48	$100.50	$100.50
Purchase #2	$147.82	9.259%	$161.5067	$161.51	$161.50	$161.50
Purchase #3	$44.95	5.673%	$47.5	$47.50	$47.50	$47.50
Purchase #4	$131.43	10.174%	$144.8017	$144.80	$144.80	$144.80
Purchase #5	$98.47	13.637%	$111.8984	$111.90	$111.90	$111.90
Purchase #6	$151.68	12.452%	$170.5672	$170.57	$170.55	$170.60
Purchase #7	$101.64	4.484%	$106.1975	$106.20	$106.20	$106.20
7 purchase totals =	$765.50		$842.9474	$842.96	$842.95	$843.00