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	$37.86	7.212%	$40.5905	$40.59	$40.60	$40.60
Purchase #2	$82.51	10.450%	$91.1323	$91.13	$91.15	$91.10
Purchase #3	$186.66	13.193%	$211.2861	$211.29	$211.30	$211.30
Purchase #4	$189.59	9.801%	$208.1717	$208.17	$208.15	$208.20
Purchase #5	$108.51	9.623%	$118.9519	$118.95	$118.95	$119.00
Purchase #6	$88.86	7.768%	$95.7626	$95.76	$95.75	$95.80
Purchase #7	$238.64	3.430%	$246.8254	$246.83	$246.85	$246.80
7 purchase totals =	$932.63		$1,012.7205	$1,012.72	$1,012.75	$1,012.80