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	$77.72	10.510%	$85.8884	$85.89	$85.90	$85.90
Purchase #2	$127.56	5.684%	$134.8105	$134.81	$134.80	$134.80
Purchase #3	$112.49	6.517%	$119.821	$119.82	$119.80	$119.80
Purchase #4	$21.96	3.549%	$22.7394	$22.74	$22.75	$22.70
Purchase #5	$89.85	12.226%	$100.8351	$100.84	$100.85	$100.80
Purchase #6	$121.73	7.165%	$130.452	$130.45	$130.45	$130.50
Purchase #7	$235.97	12.648%	$265.8155	$265.82	$265.80	$265.80
7 purchase totals =	$787.28		$860.3619	$860.37	$860.35	$860.30