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	$37.51	7.644%	$40.3773	$40.38	$40.40	$40.40
Purchase #2	$216.44	11.851%	$242.0903	$242.09	$242.10	$242.10
Purchase #3	$80.31	10.180%	$88.4856	$88.49	$88.50	$88.50
Purchase #4	$86.68	4.600%	$90.6673	$90.67	$90.65	$90.70
Purchase #5	$156.65	5.429%	$165.1545	$165.15	$165.15	$165.20
Purchase #6	$51.93	6.796%	$55.4592	$55.46	$55.45	$55.50
Purchase #7	$249.99	8.870%	$272.1641	$272.16	$272.15	$272.20
7 purchase totals =	$879.51		$954.3983	$954.40	$954.40	$954.60