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	$106.48	12.294%	$119.5707	$119.57	$119.55	$119.60
Purchase #2	$101.57	3.529%	$105.1544	$105.15	$105.15	$105.20
Purchase #3	$101.66	9.270%	$111.0839	$111.08	$111.10	$111.10
Purchase #4	$76.68	13.280%	$86.8631	$86.86	$86.85	$86.90
Purchase #5	$134.86	6.468%	$143.5827	$143.58	$143.60	$143.60
Purchase #6	$36.95	11.303%	$41.1265	$41.13	$41.15	$41.10
Purchase #7	$215.71	13.267%	$244.3282	$244.33	$244.35	$244.30
7 purchase totals =	$773.91		$851.7095	$851.70	$851.75	$851.80