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	$76.84	7.127%	$82.3164	$82.32	$82.30	$82.30
Purchase #2	$187.62	9.193%	$204.8679	$204.87	$204.85	$204.90
Purchase #3	$231.85	8.115%	$250.6646	$250.66	$250.65	$250.70
Purchase #4	$50.48	7.859%	$54.4472	$54.45	$54.45	$54.40
Purchase #5	$56.76	13.724%	$64.5497	$64.55	$64.55	$64.50
Purchase #6	$40.65	11.342%	$45.2605	$45.26	$45.25	$45.30
Purchase #7	$139.72	11.827%	$156.2447	$156.24	$156.25	$156.20
7 purchase totals =	$783.92		$858.3510	$858.35	$858.30	$858.30