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	$82.52	9.520%	$90.3759	$90.38	$90.40	$90.40
Purchase #2	$215.72	10.303%	$237.9456	$237.95	$237.95	$237.90
Purchase #3	$143.89	4.601%	$150.5104	$150.51	$150.50	$150.50
Purchase #4	$110.97	9.819%	$121.8661	$121.87	$121.85	$121.90
Purchase #5	$37.49	9.834%	$41.1768	$41.18	$41.20	$41.20
Purchase #6	$11.68	4.697%	$12.2286	$12.23	$12.25	$12.20
Purchase #7	$159.39	8.453%	$172.8632	$172.86	$172.85	$172.90
7 purchase totals =	$761.66		$826.9666	$826.98	$827.00	$827.00