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	$24.75	12.373%	$27.8123	$27.81	$27.80	$27.80
Purchase #2	$202.84	6.510%	$216.0449	$216.04	$216.05	$216.00
Purchase #3	$90.93	8.529%	$98.6854	$98.69	$98.70	$98.70
Purchase #4	$11.76	11.782%	$13.1456	$13.15	$13.15	$13.10
Purchase #5	$9.67	9.598%	$10.5981	$10.60	$10.60	$10.60
Purchase #6	$162.77	7.738%	$175.3651	$175.37	$175.35	$175.40
Purchase #7	$111.28	11.214%	$123.7589	$123.76	$123.75	$123.80
7 purchase totals =	$614.00		$665.4103	$665.42	$665.40	$665.40