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	$226.31	4.484%	$236.4577	$236.46	$236.45	$236.50
Purchase #2	$108.25	11.441%	$120.6349	$120.63	$120.65	$120.60
Purchase #3	$179.32	9.312%	$196.0183	$196.02	$196.00	$196.00
Purchase #4	$56.40	9.154%	$61.5629	$61.56	$61.55	$61.60
Purchase #5	$79.68	13.679%	$90.5794	$90.58	$90.60	$90.60
Purchase #6	$180.48	6.338%	$191.9188	$191.92	$191.90	$191.90
Purchase #7	$79.76	9.460%	$87.3053	$87.31	$87.30	$87.30
7 purchase totals =	$910.20		$984.4773	$984.48	$984.45	$984.50