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	$239.33	4.443%	$249.9634	$249.96	$249.95	$250.00
Purchase #2	$137.99	8.294%	$149.4349	$149.43	$149.45	$149.40
Purchase #3	$114.69	10.758%	$127.0284	$127.03	$127.05	$127.00
Purchase #4	$44.50	11.446%	$49.5935	$49.59	$49.60	$49.60
Purchase #5	$240.51	11.791%	$268.8685	$268.87	$268.85	$268.90
Purchase #6	$152.41	10.490%	$168.3978	$168.40	$168.40	$168.40
Purchase #7	$122.42	7.126%	$131.1436	$131.14	$131.15	$131.10
7 purchase totals =	$1,051.85		$1,144.4301	$1,144.42	$1,144.45	$1,144.40