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	$6.90	13.337%	$7.8203	$7.82	$7.80	$7.80
Purchase #2	$201.26	3.459%	$208.2216	$208.22	$208.20	$208.20
Purchase #3	$235.50	12.408%	$264.7208	$264.72	$264.70	$264.70
Purchase #4	$127.47	3.823%	$132.3432	$132.34	$132.35	$132.30
Purchase #5	$241.27	3.212%	$249.0196	$249.02	$249.00	$249.00
Purchase #6	$105.99	5.176%	$111.476	$111.48	$111.50	$111.50
Purchase #7	$193.83	10.319%	$213.8313	$213.83	$213.85	$213.80
7 purchase totals =	$1,112.22		$1,187.4328	$1,187.43	$1,187.40	$1,187.30