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	$19.98	5.854%	$21.1496	$21.15	$21.15	$21.10
Purchase #2	$88.51	10.630%	$97.9186	$97.92	$97.90	$97.90
Purchase #3	$62.44	6.754%	$66.6572	$66.66	$66.65	$66.70
Purchase #4	$54.72	3.200%	$56.471	$56.47	$56.45	$56.50
Purchase #5	$154.25	8.799%	$167.8225	$167.82	$167.80	$167.80
Purchase #6	$155.56	6.247%	$165.2778	$165.28	$165.30	$165.30
Purchase #7	$233.29	10.866%	$258.6393	$258.64	$258.65	$258.60
7 purchase totals =	$768.75		$833.9360	$833.94	$833.90	$833.90