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	$18.34	7.819%	$19.774	$19.77	$19.75	$19.80
Purchase #2	$202.87	6.478%	$216.0119	$216.01	$216.00	$216.00
Purchase #3	$208.66	11.788%	$233.2568	$233.26	$233.25	$233.30
Purchase #4	$190.44	9.685%	$208.8841	$208.88	$208.90	$208.90
Purchase #5	$188.58	4.379%	$196.8379	$196.84	$196.85	$196.80
Purchase #6	$83.57	11.608%	$93.2708	$93.27	$93.25	$93.30
Purchase #7	$68.81	3.858%	$71.4647	$71.46	$71.45	$71.50
7 purchase totals =	$961.27		$1,039.5002	$1,039.49	$1,039.45	$1,039.60