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	$66.79	10.271%	$73.65	$73.65	$73.65	$73.70
Purchase #2	$147.84	12.830%	$166.8079	$166.81	$166.80	$166.80
Purchase #3	$222.55	9.564%	$243.8347	$243.83	$243.85	$243.80
Purchase #4	$151.92	10.542%	$167.9354	$167.94	$167.95	$167.90
Purchase #5	$234.87	10.287%	$259.0311	$259.03	$259.05	$259.00
Purchase #6	$173.53	6.341%	$184.5335	$184.53	$184.55	$184.50
Purchase #7	$112.34	13.163%	$127.1273	$127.13	$127.15	$127.10
7 purchase totals =	$1,109.84		$1,222.9199	$1,222.92	$1,223.00	$1,222.80