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	$198.59	13.568%	$225.5347	$225.53	$225.55	$225.50
Purchase #2	$47.97	9.546%	$52.5492	$52.55	$52.55	$52.50
Purchase #3	$139.25	6.587%	$148.4224	$148.42	$148.40	$148.40
Purchase #4	$172.70	6.792%	$184.4298	$184.43	$184.45	$184.40
Purchase #5	$35.91	12.672%	$40.4605	$40.46	$40.45	$40.50
Purchase #6	$71.90	4.528%	$75.1556	$75.16	$75.15	$75.20
Purchase #7	$16.45	9.709%	$18.0471	$18.05	$18.05	$18.00
7 purchase totals =	$682.77		$744.5993	$744.60	$744.60	$744.50