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	$249.33	12.544%	$280.606	$280.61	$280.60	$280.60
Purchase #2	$103.73	12.542%	$116.7398	$116.74	$116.75	$116.70
Purchase #3	$211.67	9.323%	$231.404	$231.40	$231.40	$231.40
Purchase #4	$206.79	8.272%	$223.8957	$223.90	$223.90	$223.90
Purchase #5	$231.80	5.648%	$244.8921	$244.89	$244.90	$244.90
Purchase #6	$161.29	5.594%	$170.3126	$170.31	$170.30	$170.30
Purchase #7	$198.87	12.518%	$223.7645	$223.76	$223.75	$223.80
7 purchase totals =	$1,363.48		$1,491.6147	$1,491.61	$1,491.60	$1,491.60