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	$73.38	9.222%	$80.1471	$80.15	$80.15	$80.10
Purchase #2	$196.71	10.684%	$217.7265	$217.73	$217.75	$217.70
Purchase #3	$244.74	12.182%	$274.5542	$274.55	$274.55	$274.60
Purchase #4	$55.71	7.211%	$59.7272	$59.73	$59.75	$59.70
Purchase #5	$223.98	4.741%	$234.5989	$234.60	$234.60	$234.60
Purchase #6	$124.40	6.714%	$132.7522	$132.75	$132.75	$132.80
Purchase #7	$78.45	8.486%	$85.1073	$85.11	$85.10	$85.10
7 purchase totals =	$997.37		$1,084.6134	$1,084.62	$1,084.65	$1,084.60