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	$80.87	11.861%	$90.462	$90.46	$90.45	$90.50
Purchase #2	$157.76	5.860%	$167.0047	$167.00	$167.00	$167.00
Purchase #3	$101.86	10.552%	$112.6083	$112.61	$112.60	$112.60
Purchase #4	$99.98	13.632%	$113.6093	$113.61	$113.60	$113.60
Purchase #5	$151.28	3.392%	$156.4114	$156.41	$156.40	$156.40
Purchase #6	$120.56	7.249%	$129.2994	$129.30	$129.30	$129.30
Purchase #7	$111.96	12.359%	$125.7971	$125.80	$125.80	$125.80
7 purchase totals =	$824.27		$895.1922	$895.19	$895.15	$895.20