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	$100.86	6.403%	$107.3181	$107.32	$107.30	$107.30
Purchase #2	$248.55	6.550%	$264.83	$264.83	$264.85	$264.80
Purchase #3	$85.34	11.593%	$95.2335	$95.23	$95.25	$95.20
Purchase #4	$146.50	10.133%	$161.3448	$161.34	$161.35	$161.30
Purchase #5	$145.39	13.164%	$164.5291	$164.53	$164.55	$164.50
Purchase #6	$39.83	5.556%	$42.043	$42.04	$42.05	$42.00
Purchase #7	$70.95	3.212%	$73.2289	$73.23	$73.25	$73.20
7 purchase totals =	$837.42		$908.5274	$908.52	$908.60	$908.30