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	$247.58	10.208%	$272.853	$272.85	$272.85	$272.90
Purchase #2	$55.77	12.542%	$62.7647	$62.76	$62.75	$62.80
Purchase #3	$84.61	12.624%	$95.2912	$95.29	$95.30	$95.30
Purchase #4	$81.37	4.678%	$85.1765	$85.18	$85.20	$85.20
Purchase #5	$17.79	12.859%	$20.0776	$20.08	$20.10	$20.10
Purchase #6	$106.34	9.610%	$116.5593	$116.56	$116.55	$116.60
Purchase #7	$170.92	5.616%	$180.5189	$180.52	$180.50	$180.50
7 purchase totals =	$764.38		$833.2412	$833.24	$833.25	$833.40