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	$142.55	12.255%	$160.0195	$160.02	$160.00	$160.00
Purchase #2	$234.41	11.479%	$261.3179	$261.32	$261.30	$261.30
Purchase #3	$71.78	5.789%	$75.9353	$75.94	$75.95	$75.90
Purchase #4	$55.51	13.323%	$62.9056	$62.91	$62.90	$62.90
Purchase #5	$177.65	10.769%	$196.7811	$196.78	$196.80	$196.80
Purchase #6	$81.60	11.594%	$91.0607	$91.06	$91.05	$91.10
Purchase #7	$21.43	13.235%	$24.2663	$24.27	$24.25	$24.30
7 purchase totals =	$784.93		$872.2864	$872.30	$872.25	$872.30