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	$26.98	10.139%	$29.7155	$29.72	$29.70	$29.70
Purchase #2	$105.92	5.356%	$111.5931	$111.59	$111.60	$111.60
Purchase #3	$124.72	3.484%	$129.0652	$129.07	$129.05	$129.10
Purchase #4	$170.72	11.304%	$190.0182	$190.02	$190.00	$190.00
Purchase #5	$31.86	12.834%	$35.9489	$35.95	$35.95	$35.90
Purchase #6	$208.73	6.737%	$222.7921	$222.79	$222.80	$222.80
Purchase #7	$53.57	8.425%	$58.0833	$58.08	$58.10	$58.10
7 purchase totals =	$722.50		$777.2163	$777.22	$777.20	$777.20