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	$38.57	7.292%	$41.3825	$41.38	$41.40	$41.40
Purchase #2	$212.55	9.646%	$233.0526	$233.05	$233.05	$233.10
Purchase #3	$96.86	6.354%	$103.0145	$103.01	$103.00	$103.00
Purchase #4	$8.37	13.493%	$9.4994	$9.50	$9.50	$9.50
Purchase #5	$199.82	5.134%	$210.0788	$210.08	$210.10	$210.10
Purchase #6	$97.89	5.293%	$103.0713	$103.07	$103.05	$103.10
Purchase #7	$85.41	4.265%	$89.0527	$89.05	$89.05	$89.10
7 purchase totals =	$739.47		$789.1518	$789.14	$789.15	$789.30