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	$28.56	13.599%	$32.4439	$32.44	$32.45	$32.40
Purchase #2	$171.92	8.547%	$186.614	$186.61	$186.60	$186.60
Purchase #3	$40.98	3.763%	$42.5221	$42.52	$42.50	$42.50
Purchase #4	$12.54	5.760%	$13.2623	$13.26	$13.25	$13.30
Purchase #5	$190.27	11.648%	$212.4326	$212.43	$212.45	$212.40
Purchase #6	$183.67	5.849%	$194.4129	$194.41	$194.40	$194.40
Purchase #7	$242.81	5.266%	$255.5964	$255.60	$255.60	$255.60
7 purchase totals =	$870.75		$937.2842	$937.27	$937.25	$937.20