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	$123.37	6.353%	$131.2077	$131.21	$131.20	$131.20
Purchase #2	$41.92	6.211%	$44.5237	$44.52	$44.50	$44.50
Purchase #3	$238.73	12.829%	$269.3567	$269.36	$269.35	$269.40
Purchase #4	$151.75	10.700%	$167.9873	$167.99	$168.00	$168.00
Purchase #5	$14.32	5.859%	$15.159	$15.16	$15.15	$15.20
Purchase #6	$75.64	4.250%	$78.8547	$78.85	$78.85	$78.90
Purchase #7	$70.43	9.512%	$77.1293	$77.13	$77.15	$77.10
7 purchase totals =	$716.16		$784.2184	$784.22	$784.20	$784.30