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	$17.54	4.287%	$18.2919	$18.29	$18.30	$18.30
Purchase #2	$33.25	6.417%	$35.3837	$35.38	$35.40	$35.40
Purchase #3	$80.75	4.759%	$84.5929	$84.59	$84.60	$84.60
Purchase #4	$143.89	3.253%	$148.5707	$148.57	$148.55	$148.60
Purchase #5	$84.41	5.819%	$89.3218	$89.32	$89.30	$89.30
Purchase #6	$227.57	13.819%	$259.0179	$259.02	$259.00	$259.00
Purchase #7	$64.29	9.122%	$70.1545	$70.15	$70.15	$70.20
7 purchase totals =	$651.70		$705.3334	$705.32	$705.30	$705.40