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	$226.92	5.588%	$239.6003	$239.60	$239.60	$239.60
Purchase #2	$35.82	6.310%	$38.0802	$38.08	$38.10	$38.10
Purchase #3	$146.66	12.427%	$164.8854	$164.89	$164.90	$164.90
Purchase #4	$54.81	8.717%	$59.5878	$59.59	$59.60	$59.60
Purchase #5	$171.76	10.271%	$189.4015	$189.40	$189.40	$189.40
Purchase #6	$186.89	5.245%	$196.6924	$196.69	$196.70	$196.70
Purchase #7	$221.93	4.353%	$231.5906	$231.59	$231.60	$231.60
7 purchase totals =	$1,044.79		$1,119.8382	$1,119.84	$1,119.90	$1,119.90