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	$239.69	6.608%	$255.5287	$255.53	$255.55	$255.50
Purchase #2	$226.84	8.263%	$245.5838	$245.58	$245.60	$245.60
Purchase #3	$214.27	13.693%	$243.61	$243.61	$243.60	$243.60
Purchase #4	$42.76	13.627%	$48.5869	$48.59	$48.60	$48.60
Purchase #5	$246.40	8.165%	$266.5186	$266.52	$266.50	$266.50
Purchase #6	$138.55	12.508%	$155.8798	$155.88	$155.90	$155.90
Purchase #7	$145.85	13.747%	$165.9	$165.90	$165.90	$165.90
7 purchase totals =	$1,254.36		$1,381.6078	$1,381.61	$1,381.65	$1,381.60