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	$173.34	10.586%	$191.6898	$191.69	$191.70	$191.70
Purchase #2	$200.70	9.699%	$220.1659	$220.17	$220.15	$220.20
Purchase #3	$140.60	6.853%	$150.2353	$150.24	$150.25	$150.20
Purchase #4	$78.63	6.276%	$83.5648	$83.56	$83.55	$83.60
Purchase #5	$178.45	12.408%	$200.5921	$200.59	$200.60	$200.60
Purchase #6	$24.50	11.615%	$27.3457	$27.35	$27.35	$27.30
Purchase #7	$62.34	10.477%	$68.8714	$68.87	$68.85	$68.90
7 purchase totals =	$858.56		$942.4650	$942.47	$942.45	$942.50