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	$40.31	5.162%	$42.3908	$42.39	$42.40	$42.40
Purchase #2	$155.27	10.432%	$171.4678	$171.47	$171.45	$171.50
Purchase #3	$46.59	7.374%	$50.0255	$50.03	$50.05	$50.00
Purchase #4	$194.40	11.837%	$217.4111	$217.41	$217.40	$217.40
Purchase #5	$11.96	12.279%	$13.4286	$13.43	$13.45	$13.40
Purchase #6	$144.29	10.656%	$159.6655	$159.67	$159.65	$159.70
Purchase #7	$172.79	11.398%	$192.4846	$192.48	$192.50	$192.50
7 purchase totals =	$765.61		$846.8739	$846.88	$846.90	$846.90