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	$105.33	13.153%	$119.1841	$119.18	$119.20	$119.20
Purchase #2	$148.69	6.646%	$158.5719	$158.57	$158.55	$158.60
Purchase #3	$138.68	8.387%	$150.3111	$150.31	$150.30	$150.30
Purchase #4	$34.45	10.369%	$38.0221	$38.02	$38.00	$38.00
Purchase #5	$131.86	4.395%	$137.6552	$137.66	$137.65	$137.70
Purchase #6	$238.25	6.580%	$253.9269	$253.93	$253.95	$253.90
Purchase #7	$19.33	6.414%	$20.5698	$20.57	$20.55	$20.60
7 purchase totals =	$816.59		$878.2411	$878.24	$878.20	$878.30