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	$48.50	6.578%	$51.6903	$51.69	$51.70	$51.70
Purchase #2	$57.90	12.403%	$65.0813	$65.08	$65.10	$65.10
Purchase #3	$179.44	9.741%	$196.9193	$196.92	$196.90	$196.90
Purchase #4	$125.29	6.244%	$133.1131	$133.11	$133.10	$133.10
Purchase #5	$48.85	13.801%	$55.5918	$55.59	$55.60	$55.60
Purchase #6	$158.78	5.485%	$167.4891	$167.49	$167.50	$167.50
Purchase #7	$70.34	6.457%	$74.8819	$74.88	$74.90	$74.90
7 purchase totals =	$689.10		$744.7668	$744.76	$744.80	$744.80