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	$27.80	13.409%	$31.5277	$31.53	$31.55	$31.50
Purchase #2	$71.64	9.764%	$78.6349	$78.63	$78.65	$78.60
Purchase #3	$122.86	11.348%	$136.8022	$136.80	$136.80	$136.80
Purchase #4	$83.35	6.480%	$88.7511	$88.75	$88.75	$88.80
Purchase #5	$213.63	12.395%	$240.1094	$240.11	$240.10	$240.10
Purchase #6	$100.32	12.456%	$112.8159	$112.82	$112.80	$112.80
Purchase #7	$49.46	11.155%	$54.9773	$54.98	$55.00	$55.00
7 purchase totals =	$669.06		$743.6185	$743.62	$743.65	$743.60