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	$142.68	8.127%	$154.2756	$154.28	$154.30	$154.30
Purchase #2	$77.42	6.671%	$82.5847	$82.58	$82.60	$82.60
Purchase #3	$246.78	13.588%	$280.3125	$280.31	$280.30	$280.30
Purchase #4	$174.61	8.676%	$189.7592	$189.76	$189.75	$189.80
Purchase #5	$125.34	12.702%	$141.2607	$141.26	$141.25	$141.30
Purchase #6	$33.37	9.254%	$36.4581	$36.46	$36.45	$36.50
Purchase #7	$126.38	7.668%	$136.0708	$136.07	$136.05	$136.10
7 purchase totals =	$926.58		$1,020.7216	$1,020.72	$1,020.70	$1,020.90