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	$219.89	12.667%	$247.7435	$247.74	$247.75	$247.70
Purchase #2	$168.79	10.425%	$186.3864	$186.39	$186.40	$186.40
Purchase #3	$176.55	13.503%	$200.3895	$200.39	$200.40	$200.40
Purchase #4	$149.69	12.391%	$168.2381	$168.24	$168.25	$168.20
Purchase #5	$118.76	4.542%	$124.1541	$124.15	$124.15	$124.20
Purchase #6	$228.55	4.773%	$239.4587	$239.46	$239.45	$239.50
Purchase #7	$210.69	10.835%	$233.5183	$233.52	$233.50	$233.50
7 purchase totals =	$1,272.92		$1,399.8886	$1,399.89	$1,399.90	$1,399.90