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	$44.47	12.791%	$50.1582	$50.16	$50.15	$50.20
Purchase #2	$238.82	13.874%	$271.9539	$271.95	$271.95	$272.00
Purchase #3	$170.28	3.843%	$176.8239	$176.82	$176.80	$176.80
Purchase #4	$129.93	13.364%	$147.2938	$147.29	$147.30	$147.30
Purchase #5	$86.28	4.157%	$89.8667	$89.87	$89.85	$89.90
Purchase #6	$67.77	7.659%	$72.9605	$72.96	$72.95	$73.00
Purchase #7	$87.42	3.373%	$90.3687	$90.37	$90.35	$90.40
7 purchase totals =	$824.97		$899.4257	$899.42	$899.35	$899.60