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	$170.77	11.835%	$190.9806	$190.98	$191.00	$191.00
Purchase #2	$16.34	9.508%	$17.8936	$17.89	$17.90	$17.90
Purchase #3	$139.35	10.670%	$154.2186	$154.22	$154.20	$154.20
Purchase #4	$212.78	5.564%	$224.6191	$224.62	$224.60	$224.60
Purchase #5	$82.48	9.785%	$90.5507	$90.55	$90.55	$90.60
Purchase #6	$220.76	13.629%	$250.8474	$250.85	$250.85	$250.80
Purchase #7	$108.78	11.709%	$121.5171	$121.52	$121.50	$121.50
7 purchase totals =	$951.26		$1,050.6271	$1,050.63	$1,050.60	$1,050.60