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	$28.45	12.557%	$32.0225	$32.02	$32.00	$32.00
Purchase #2	$117.83	13.862%	$134.1636	$134.16	$134.15	$134.20
Purchase #3	$215.62	6.869%	$230.4309	$230.43	$230.45	$230.40
Purchase #4	$157.46	6.326%	$167.4209	$167.42	$167.40	$167.40
Purchase #5	$62.67	8.348%	$67.9017	$67.90	$67.90	$67.90
Purchase #6	$88.69	6.128%	$94.1249	$94.12	$94.10	$94.10
Purchase #7	$54.76	8.553%	$59.4436	$59.44	$59.45	$59.40
7 purchase totals =	$725.48		$785.5081	$785.49	$785.45	$785.40