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	$115.54	11.849%	$129.2303	$129.23	$129.25	$129.20
Purchase #2	$122.50	10.454%	$135.3062	$135.31	$135.30	$135.30
Purchase #3	$101.32	7.565%	$108.9849	$108.98	$109.00	$109.00
Purchase #4	$94.59	6.628%	$100.8594	$100.86	$100.85	$100.90
Purchase #5	$106.80	11.788%	$119.3896	$119.39	$119.40	$119.40
Purchase #6	$223.89	10.556%	$247.5238	$247.52	$247.50	$247.50
Purchase #7	$31.39	10.294%	$34.6213	$34.62	$34.60	$34.60
7 purchase totals =	$796.03		$875.9155	$875.91	$875.90	$875.90