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	$51.47	10.504%	$56.8764	$56.88	$56.90	$56.90
Purchase #2	$185.76	9.855%	$204.0666	$204.07	$204.05	$204.10
Purchase #3	$217.36	13.238%	$246.1341	$246.13	$246.15	$246.10
Purchase #4	$52.61	13.367%	$59.6424	$59.64	$59.65	$59.60
Purchase #5	$25.81	12.833%	$29.1222	$29.12	$29.10	$29.10
Purchase #6	$221.59	3.153%	$228.5767	$228.58	$228.60	$228.60
Purchase #7	$79.52	12.706%	$89.6238	$89.62	$89.60	$89.60
7 purchase totals =	$834.12		$914.0422	$914.04	$914.05	$914.00