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	$56.32	12.802%	$63.5301	$63.53	$63.55	$63.50
Purchase #2	$204.33	8.761%	$222.2314	$222.23	$222.25	$222.20
Purchase #3	$103.91	3.847%	$107.9074	$107.91	$107.90	$107.90
Purchase #4	$88.47	3.311%	$91.3992	$91.40	$91.40	$91.40
Purchase #5	$169.85	9.409%	$185.8312	$185.83	$185.85	$185.80
Purchase #6	$81.87	11.480%	$91.2687	$91.27	$91.25	$91.30
Purchase #7	$15.56	11.752%	$17.3886	$17.39	$17.40	$17.40
7 purchase totals =	$720.31		$779.5566	$779.56	$779.60	$779.50