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	$25.66	5.259%	$27.0095	$27.01	$27.00	$27.00
Purchase #2	$34.90	10.301%	$38.495	$38.50	$38.50	$38.50
Purchase #3	$241.30	3.339%	$249.357	$249.36	$249.35	$249.40
Purchase #4	$160.90	4.205%	$167.6658	$167.67	$167.65	$167.70
Purchase #5	$56.63	11.672%	$63.2399	$63.24	$63.25	$63.20
Purchase #6	$224.84	8.468%	$243.8795	$243.88	$243.90	$243.90
Purchase #7	$40.89	12.256%	$45.9015	$45.90	$45.90	$45.90
7 purchase totals =	$785.12		$835.5482	$835.56	$835.55	$835.60