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	$68.74	5.441%	$72.4801	$72.48	$72.50	$72.50
Purchase #2	$129.32	10.178%	$142.4822	$142.48	$142.50	$142.50
Purchase #3	$248.59	8.799%	$270.4634	$270.46	$270.45	$270.50
Purchase #4	$139.88	3.513%	$144.794	$144.79	$144.80	$144.80
Purchase #5	$54.65	13.544%	$62.0518	$62.05	$62.05	$62.10
Purchase #6	$110.52	6.750%	$117.9801	$117.98	$118.00	$118.00
Purchase #7	$45.53	11.603%	$50.8128	$50.81	$50.80	$50.80
7 purchase totals =	$797.23		$861.0644	$861.05	$861.10	$861.20