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	$124.82	3.583%	$129.2923	$129.29	$129.30	$129.30
Purchase #2	$48.40	6.126%	$51.365	$51.37	$51.35	$51.40
Purchase #3	$17.69	13.738%	$20.1203	$20.12	$20.10	$20.10
Purchase #4	$129.86	9.796%	$142.5811	$142.58	$142.60	$142.60
Purchase #5	$238.58	12.279%	$267.8752	$267.88	$267.90	$267.90
Purchase #6	$177.61	10.833%	$196.8505	$196.85	$196.85	$196.90
Purchase #7	$60.50	4.855%	$63.4373	$63.44	$63.45	$63.40
7 purchase totals =	$797.46		$871.5217	$871.53	$871.55	$871.60