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	$167.56	6.709%	$178.8016	$178.80	$178.80	$178.80
Purchase #2	$53.37	11.759%	$59.6458	$59.65	$59.65	$59.60
Purchase #3	$175.27	7.861%	$189.048	$189.05	$189.05	$189.00
Purchase #4	$67.27	12.435%	$75.635	$75.64	$75.65	$75.60
Purchase #5	$132.99	11.452%	$148.22	$148.22	$148.20	$148.20
Purchase #6	$153.69	12.124%	$172.3234	$172.32	$172.30	$172.30
Purchase #7	$35.56	11.483%	$39.6434	$39.64	$39.65	$39.60
7 purchase totals =	$785.71		$863.3172	$863.32	$863.30	$863.10