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	$135.92	6.543%	$144.8132	$144.81	$144.80	$144.80
Purchase #2	$119.36	3.328%	$123.3323	$123.33	$123.35	$123.30
Purchase #3	$134.95	13.176%	$152.731	$152.73	$152.75	$152.70
Purchase #4	$94.77	5.308%	$99.8004	$99.80	$99.80	$99.80
Purchase #5	$56.52	5.586%	$59.6772	$59.68	$59.70	$59.70
Purchase #6	$104.66	4.116%	$108.9678	$108.97	$108.95	$109.00
Purchase #7	$58.80	11.340%	$65.4679	$65.47	$65.45	$65.50
7 purchase totals =	$704.98		$754.7898	$754.79	$754.80	$754.80