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	$166.91	3.299%	$172.4164	$172.42	$172.40	$172.40
Purchase #2	$161.62	12.332%	$181.551	$181.55	$181.55	$181.60
Purchase #3	$35.98	12.870%	$40.6106	$40.61	$40.60	$40.60
Purchase #4	$125.45	5.527%	$132.3836	$132.38	$132.40	$132.40
Purchase #5	$179.42	9.654%	$196.7412	$196.74	$196.75	$196.70
Purchase #6	$179.73	7.836%	$193.8136	$193.81	$193.80	$193.80
Purchase #7	$35.77	12.410%	$40.2091	$40.21	$40.20	$40.20
7 purchase totals =	$884.88		$957.7255	$957.72	$957.70	$957.70