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	$53.34	3.854%	$55.3957	$55.40	$55.40	$55.40
Purchase #2	$105.82	12.674%	$119.2316	$119.23	$119.25	$119.20
Purchase #3	$67.45	4.778%	$70.6728	$70.67	$70.65	$70.70
Purchase #4	$126.32	12.758%	$142.4359	$142.44	$142.45	$142.40
Purchase #5	$85.57	6.506%	$91.1372	$91.14	$91.15	$91.10
Purchase #6	$40.28	7.422%	$43.2696	$43.27	$43.25	$43.30
Purchase #7	$30.34	12.156%	$34.0281	$34.03	$34.05	$34.00
7 purchase totals =	$509.12		$556.1709	$556.18	$556.20	$556.10