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	$7.89	11.624%	$8.8071	$8.81	$8.80	$8.80
Purchase #2	$229.54	8.874%	$249.9094	$249.91	$249.90	$249.90
Purchase #3	$40.26	13.817%	$45.8227	$45.82	$45.80	$45.80
Purchase #4	$126.89	9.623%	$139.1006	$139.10	$139.10	$139.10
Purchase #5	$18.90	13.245%	$21.4033	$21.40	$21.40	$21.40
Purchase #6	$59.85	13.826%	$68.1249	$68.12	$68.10	$68.10
Purchase #7	$172.85	13.650%	$196.444	$196.44	$196.45	$196.40
7 purchase totals =	$656.18		$729.6120	$729.60	$729.55	$729.50