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	$114.45	4.250%	$119.3141	$119.31	$119.30	$119.30
Purchase #2	$49.35	13.696%	$56.109	$56.11	$56.10	$56.10
Purchase #3	$48.75	9.627%	$53.4432	$53.44	$53.45	$53.40
Purchase #4	$234.93	8.741%	$255.4652	$255.47	$255.45	$255.50
Purchase #5	$42.82	3.133%	$44.1616	$44.16	$44.15	$44.20
Purchase #6	$137.97	12.688%	$155.4756	$155.48	$155.50	$155.50
Purchase #7	$101.25	9.245%	$110.6106	$110.61	$110.60	$110.60
7 purchase totals =	$729.52		$794.5793	$794.58	$794.55	$794.60