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	$152.76	12.122%	$171.2776	$171.28	$171.30	$171.30
Purchase #2	$249.82	3.476%	$258.5037	$258.50	$258.50	$258.50
Purchase #3	$103.83	13.717%	$118.0724	$118.07	$118.05	$118.10
Purchase #4	$180.75	3.140%	$186.4256	$186.43	$186.45	$186.40
Purchase #5	$12.72	9.281%	$13.9005	$13.90	$13.90	$13.90
Purchase #6	$186.49	5.574%	$196.885	$196.89	$196.90	$196.90
Purchase #7	$32.80	12.223%	$36.8091	$36.81	$36.80	$36.80
7 purchase totals =	$919.17		$981.8739	$981.88	$981.90	$981.90