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	$21.32	3.859%	$22.1427	$22.14	$22.15	$22.10
Purchase #2	$80.30	12.530%	$90.3616	$90.36	$90.35	$90.40
Purchase #3	$164.54	8.238%	$178.0948	$178.09	$178.10	$178.10
Purchase #4	$90.33	9.508%	$98.9186	$98.92	$98.90	$98.90
Purchase #5	$224.62	4.541%	$234.82	$234.82	$234.80	$234.80
Purchase #6	$104.50	12.739%	$117.8123	$117.81	$117.80	$117.80
Purchase #7	$194.72	7.356%	$209.0436	$209.04	$209.05	$209.00
7 purchase totals =	$880.33		$951.1936	$951.18	$951.15	$951.10