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	$5.37	7.861%	$5.7921	$5.79	$5.80	$5.80
Purchase #2	$249.32	5.277%	$262.4766	$262.48	$262.50	$262.50
Purchase #3	$235.92	12.445%	$265.2802	$265.28	$265.30	$265.30
Purchase #4	$219.82	12.144%	$246.5149	$246.51	$246.50	$246.50
Purchase #5	$162.62	5.774%	$172.0097	$172.01	$172.00	$172.00
Purchase #6	$99.38	11.708%	$111.0154	$111.02	$111.00	$111.00
Purchase #7	$12.91	6.282%	$13.721	$13.72	$13.70	$13.70
7 purchase totals =	$985.34		$1,076.8099	$1,076.81	$1,076.80	$1,076.80