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	$246.71	11.272%	$274.5192	$274.52	$274.50	$274.50
Purchase #2	$47.84	13.552%	$54.3233	$54.32	$54.30	$54.30
Purchase #3	$41.27	12.147%	$46.2831	$46.28	$46.30	$46.30
Purchase #4	$186.90	7.275%	$200.497	$200.50	$200.50	$200.50
Purchase #5	$17.41	11.399%	$19.3946	$19.39	$19.40	$19.40
Purchase #6	$72.63	5.490%	$76.6174	$76.62	$76.60	$76.60
Purchase #7	$233.90	13.558%	$265.6122	$265.61	$265.60	$265.60
7 purchase totals =	$846.66		$937.2468	$937.24	$937.20	$937.20