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	$39.62	6.509%	$42.1989	$42.20	$42.20	$42.20
Purchase #2	$204.77	12.756%	$230.8905	$230.89	$230.90	$230.90
Purchase #3	$37.89	6.216%	$40.2452	$40.25	$40.25	$40.20
Purchase #4	$97.75	13.571%	$111.0157	$111.02	$111.00	$111.00
Purchase #5	$196.86	13.671%	$223.7727	$223.77	$223.75	$223.80
Purchase #6	$30.85	7.494%	$33.1619	$33.16	$33.15	$33.20
Purchase #7	$160.76	6.528%	$171.2544	$171.25	$171.25	$171.30
7 purchase totals =	$768.50		$852.5393	$852.54	$852.50	$852.60