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	$125.36	8.605%	$136.1472	$136.15	$136.15	$136.10
Purchase #2	$49.27	9.610%	$54.0048	$54.00	$54.00	$54.00
Purchase #3	$167.68	11.856%	$187.5601	$187.56	$187.55	$187.60
Purchase #4	$56.37	11.536%	$62.8728	$62.87	$62.85	$62.90
Purchase #5	$53.59	11.167%	$59.5744	$59.57	$59.55	$59.60
Purchase #6	$157.49	7.245%	$168.9002	$168.90	$168.90	$168.90
Purchase #7	$215.57	4.259%	$224.7511	$224.75	$224.75	$224.80
7 purchase totals =	$825.33		$893.8106	$893.80	$893.75	$893.90