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	$79.64	6.181%	$84.5625	$84.56	$84.55	$84.60
Purchase #2	$99.91	5.482%	$105.3871	$105.39	$105.40	$105.40
Purchase #3	$142.55	12.444%	$160.2889	$160.29	$160.30	$160.30
Purchase #4	$41.89	9.672%	$45.9416	$45.94	$45.95	$45.90
Purchase #5	$240.56	5.739%	$254.3657	$254.37	$254.35	$254.40
Purchase #6	$205.96	4.554%	$215.3394	$215.34	$215.35	$215.30
Purchase #7	$33.56	10.556%	$37.1026	$37.10	$37.10	$37.10
7 purchase totals =	$844.07		$902.9878	$902.99	$903.00	$903.00