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	$224.34	6.152%	$238.1414	$238.14	$238.15	$238.10
Purchase #2	$184.50	9.256%	$201.5773	$201.58	$201.60	$201.60
Purchase #3	$111.85	11.279%	$124.4656	$124.47	$124.45	$124.50
Purchase #4	$171.40	11.174%	$190.5522	$190.55	$190.55	$190.60
Purchase #5	$238.45	7.141%	$255.4777	$255.48	$255.50	$255.50
Purchase #6	$31.98	10.804%	$35.4351	$35.44	$35.45	$35.40
Purchase #7	$216.43	5.406%	$228.1302	$228.13	$228.15	$228.10
7 purchase totals =	$1,178.95		$1,273.7795	$1,273.79	$1,273.85	$1,273.80