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	$20.30	6.169%	$21.5523	$21.55	$21.55	$21.60
Purchase #2	$205.66	5.668%	$217.3168	$217.32	$217.30	$217.30
Purchase #3	$178.34	6.670%	$190.2353	$190.24	$190.25	$190.20
Purchase #4	$35.58	4.644%	$37.2323	$37.23	$37.25	$37.20
Purchase #5	$113.37	11.749%	$126.6898	$126.69	$126.70	$126.70
Purchase #6	$33.46	11.785%	$37.4033	$37.40	$37.40	$37.40
Purchase #7	$129.36	5.501%	$136.4761	$136.48	$136.50	$136.50
7 purchase totals =	$716.07		$766.9059	$766.91	$766.95	$766.90