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	$112.48	8.491%	$122.0307	$122.03	$122.05	$122.00
Purchase #2	$237.71	11.393%	$264.7923	$264.79	$264.80	$264.80
Purchase #3	$67.88	5.261%	$71.4512	$71.45	$71.45	$71.50
Purchase #4	$102.96	6.469%	$109.6205	$109.62	$109.60	$109.60
Purchase #5	$130.74	6.437%	$139.1557	$139.16	$139.15	$139.20
Purchase #6	$163.80	4.281%	$170.8123	$170.81	$170.80	$170.80
Purchase #7	$19.72	9.102%	$21.5149	$21.51	$21.50	$21.50
7 purchase totals =	$835.29		$899.3776	$899.37	$899.35	$899.40