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	$144.42	13.610%	$164.0756	$164.08	$164.10	$164.10
Purchase #2	$148.84	13.760%	$169.3204	$169.32	$169.30	$169.30
Purchase #3	$140.97	4.685%	$147.5744	$147.57	$147.55	$147.60
Purchase #4	$56.65	11.832%	$63.3528	$63.35	$63.35	$63.40
Purchase #5	$126.31	7.689%	$136.022	$136.02	$136.00	$136.00
Purchase #6	$112.39	5.738%	$118.8389	$118.84	$118.85	$118.80
Purchase #7	$67.25	6.670%	$71.7356	$71.74	$71.75	$71.70
7 purchase totals =	$796.83		$870.9197	$870.92	$870.90	$870.90