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	$169.59	9.162%	$185.1278	$185.13	$185.15	$185.10
Purchase #2	$87.49	7.730%	$94.253	$94.25	$94.25	$94.30
Purchase #3	$176.88	5.657%	$186.8861	$186.89	$186.90	$186.90
Purchase #4	$28.89	9.730%	$31.701	$31.70	$31.70	$31.70
Purchase #5	$34.52	12.818%	$38.9448	$38.94	$38.95	$38.90
Purchase #6	$229.38	9.332%	$250.7857	$250.79	$250.80	$250.80
Purchase #7	$42.66	7.535%	$45.8744	$45.87	$45.85	$45.90
7 purchase totals =	$769.41		$833.5728	$833.57	$833.60	$833.60