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	$120.49	6.699%	$128.5616	$128.56	$128.55	$128.60
Purchase #2	$200.84	11.422%	$223.7799	$223.78	$223.80	$223.80
Purchase #3	$118.37	12.326%	$132.9603	$132.96	$132.95	$133.00
Purchase #4	$59.54	10.700%	$65.9108	$65.91	$65.90	$65.90
Purchase #5	$81.87	9.437%	$89.5961	$89.60	$89.60	$89.60
Purchase #6	$176.32	5.716%	$186.3985	$186.40	$186.40	$186.40
Purchase #7	$155.96	12.867%	$176.0274	$176.03	$176.05	$176.00
7 purchase totals =	$913.39		$1,003.2346	$1,003.24	$1,003.25	$1,003.30