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	$67.87	6.256%	$72.1159	$72.12	$72.10	$72.10
Purchase #2	$95.97	5.107%	$100.8712	$100.87	$100.85	$100.90
Purchase #3	$57.97	5.658%	$61.2499	$61.25	$61.25	$61.20
Purchase #4	$228.61	10.568%	$252.7695	$252.77	$252.75	$252.80
Purchase #5	$143.34	10.183%	$157.9363	$157.94	$157.95	$157.90
Purchase #6	$194.35	12.105%	$217.8761	$217.88	$217.90	$217.90
Purchase #7	$65.35	9.309%	$71.4334	$71.43	$71.45	$71.40
7 purchase totals =	$853.46		$934.2523	$934.26	$934.25	$934.20