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	$53.90	9.730%	$59.1445	$59.14	$59.15	$59.10
Purchase #2	$126.61	13.428%	$143.6112	$143.61	$143.60	$143.60
Purchase #3	$29.84	11.322%	$33.2185	$33.22	$33.20	$33.20
Purchase #4	$77.80	12.863%	$87.8074	$87.81	$87.80	$87.80
Purchase #5	$217.27	13.505%	$246.6123	$246.61	$246.60	$246.60
Purchase #6	$38.28	9.615%	$41.9606	$41.96	$41.95	$42.00
Purchase #7	$35.72	12.640%	$40.235	$40.24	$40.25	$40.20
7 purchase totals =	$579.42		$652.5895	$652.59	$652.55	$652.50