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	$86.53	13.738%	$98.4175	$98.42	$98.40	$98.40
Purchase #2	$108.94	7.791%	$117.4275	$117.43	$117.45	$117.40
Purchase #3	$82.42	11.325%	$91.7541	$91.75	$91.75	$91.80
Purchase #4	$61.43	10.555%	$67.9139	$67.91	$67.90	$67.90
Purchase #5	$102.35	4.815%	$107.2782	$107.28	$107.30	$107.30
Purchase #6	$141.35	7.590%	$152.0785	$152.08	$152.10	$152.10
Purchase #7	$105.28	4.122%	$109.6196	$109.62	$109.60	$109.60
7 purchase totals =	$688.30		$744.4893	$744.49	$744.50	$744.50