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	$53.94	13.390%	$61.1626	$61.16	$61.15	$61.20
Purchase #2	$20.43	3.380%	$21.1205	$21.12	$21.10	$21.10
Purchase #3	$105.75	4.571%	$110.5838	$110.58	$110.60	$110.60
Purchase #4	$142.91	5.579%	$150.8829	$150.88	$150.90	$150.90
Purchase #5	$123.78	6.432%	$131.7415	$131.74	$131.75	$131.70
Purchase #6	$20.54	11.732%	$22.9498	$22.95	$22.95	$22.90
Purchase #7	$13.60	4.765%	$14.248	$14.25	$14.25	$14.20
7 purchase totals =	$480.95		$512.6891	$512.68	$512.70	$512.60