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	$123.47	11.182%	$137.2764	$137.28	$137.30	$137.30
Purchase #2	$12.96	6.188%	$13.762	$13.76	$13.75	$13.80
Purchase #3	$169.67	12.437%	$190.7719	$190.77	$190.75	$190.80
Purchase #4	$233.37	7.447%	$250.7491	$250.75	$250.75	$250.70
Purchase #5	$212.58	3.700%	$220.4455	$220.45	$220.45	$220.40
Purchase #6	$63.59	13.580%	$72.2255	$72.23	$72.25	$72.20
Purchase #7	$174.76	3.158%	$180.2789	$180.28	$180.30	$180.30
7 purchase totals =	$990.40		$1,065.5093	$1,065.52	$1,065.55	$1,065.50