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	$27.62	12.613%	$31.1037	$31.10	$31.10	$31.10
Purchase #2	$118.61	6.732%	$126.5948	$126.59	$126.60	$126.60
Purchase #3	$154.76	10.638%	$171.2234	$171.22	$171.20	$171.20
Purchase #4	$74.74	3.844%	$77.613	$77.61	$77.60	$77.60
Purchase #5	$25.73	6.242%	$27.3361	$27.34	$27.35	$27.30
Purchase #6	$178.52	4.109%	$185.8554	$185.86	$185.85	$185.90
Purchase #7	$32.80	11.763%	$36.6583	$36.66	$36.65	$36.70
7 purchase totals =	$612.78		$656.3847	$656.38	$656.35	$656.40