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	$168.35	3.159%	$173.6682	$173.67	$173.65	$173.70
Purchase #2	$40.89	10.297%	$45.1004	$45.10	$45.10	$45.10
Purchase #3	$85.66	10.424%	$94.5892	$94.59	$94.60	$94.60
Purchase #4	$229.38	6.520%	$244.3356	$244.34	$244.35	$244.30
Purchase #5	$29.44	3.354%	$30.4274	$30.43	$30.45	$30.40
Purchase #6	$34.66	3.730%	$35.9528	$35.95	$35.95	$36.00
Purchase #7	$41.96	9.147%	$45.7981	$45.80	$45.80	$45.80
7 purchase totals =	$630.34		$669.8717	$669.88	$669.90	$669.90