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	$102.57	9.103%	$111.9069	$111.91	$111.90	$111.90
Purchase #2	$77.38	6.270%	$82.2317	$82.23	$82.25	$82.20
Purchase #3	$142.87	7.322%	$153.3309	$153.33	$153.35	$153.30
Purchase #4	$52.97	4.847%	$55.5375	$55.54	$55.55	$55.50
Purchase #5	$248.40	12.830%	$280.2697	$280.27	$280.25	$280.30
Purchase #6	$18.70	9.122%	$20.4058	$20.41	$20.40	$20.40
Purchase #7	$154.78	10.526%	$171.0721	$171.07	$171.05	$171.10
7 purchase totals =	$797.67		$874.7546	$874.76	$874.75	$874.70