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	$95.31	5.798%	$100.8361	$100.84	$100.85	$100.80
Purchase #2	$137.79	3.398%	$142.4721	$142.47	$142.45	$142.50
Purchase #3	$83.61	4.295%	$87.201	$87.20	$87.20	$87.20
Purchase #4	$172.47	7.738%	$185.8157	$185.82	$185.80	$185.80
Purchase #5	$153.55	9.132%	$167.5722	$167.57	$167.55	$167.60
Purchase #6	$155.63	6.172%	$165.2355	$165.24	$165.25	$165.20
Purchase #7	$221.66	6.141%	$235.2721	$235.27	$235.25	$235.30
7 purchase totals =	$1,020.02		$1,084.4047	$1,084.41	$1,084.35	$1,084.40