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	$46.51	10.369%	$51.3326	$51.33	$51.35	$51.30
Purchase #2	$240.34	9.133%	$262.2903	$262.29	$262.30	$262.30
Purchase #3	$131.32	4.328%	$137.0035	$137.00	$137.00	$137.00
Purchase #4	$53.62	11.113%	$59.5788	$59.58	$59.60	$59.60
Purchase #5	$33.54	5.143%	$35.265	$35.27	$35.25	$35.30
Purchase #6	$213.94	12.386%	$240.4386	$240.44	$240.45	$240.40
Purchase #7	$93.61	10.364%	$103.3117	$103.31	$103.30	$103.30
7 purchase totals =	$812.88		$889.2205	$889.22	$889.25	$889.20