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	$47.32	7.306%	$50.7772	$50.78	$50.80	$50.80
Purchase #2	$232.40	12.604%	$261.6917	$261.69	$261.70	$261.70
Purchase #3	$185.55	3.419%	$191.894	$191.89	$191.90	$191.90
Purchase #4	$131.51	8.442%	$142.6121	$142.61	$142.60	$142.60
Purchase #5	$60.76	13.567%	$69.0033	$69.00	$69.00	$69.00
Purchase #6	$224.83	10.326%	$248.0459	$248.05	$248.05	$248.00
Purchase #7	$105.69	13.379%	$119.8303	$119.83	$119.85	$119.80
7 purchase totals =	$988.06		$1,083.8545	$1,083.85	$1,083.90	$1,083.80