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	$249.45	11.160%	$277.2886	$277.29	$277.30	$277.30
Purchase #2	$62.80	4.347%	$65.5299	$65.53	$65.55	$65.50
Purchase #3	$18.34	3.477%	$18.9777	$18.98	$19.00	$19.00
Purchase #4	$125.71	9.715%	$137.9227	$137.92	$137.90	$137.90
Purchase #5	$50.67	4.397%	$52.898	$52.90	$52.90	$52.90
Purchase #6	$86.72	4.544%	$90.6606	$90.66	$90.65	$90.70
Purchase #7	$85.94	4.576%	$89.8726	$89.87	$89.85	$89.90
7 purchase totals =	$679.63		$733.1501	$733.15	$733.15	$733.20