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	$111.67	6.672%	$119.1206	$119.12	$119.10	$119.10
Purchase #2	$249.77	12.332%	$280.5716	$280.57	$280.55	$280.60
Purchase #3	$196.71	11.788%	$219.8982	$219.90	$219.90	$219.90
Purchase #4	$134.96	9.435%	$147.6935	$147.69	$147.70	$147.70
Purchase #5	$7.91	8.295%	$8.5661	$8.57	$8.55	$8.60
Purchase #6	$55.48	10.805%	$61.4746	$61.47	$61.45	$61.50
Purchase #7	$128.90	12.398%	$144.881	$144.88	$144.90	$144.90
7 purchase totals =	$885.40		$982.2056	$982.20	$982.15	$982.30