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	$243.44	5.185%	$256.0624	$256.06	$256.05	$256.10
Purchase #2	$102.61	6.670%	$109.4541	$109.45	$109.45	$109.50
Purchase #3	$128.86	10.252%	$142.0707	$142.07	$142.05	$142.10
Purchase #4	$88.29	5.551%	$93.191	$93.19	$93.20	$93.20
Purchase #5	$17.89	11.741%	$19.9905	$19.99	$20.00	$20.00
Purchase #6	$102.32	6.616%	$109.0895	$109.09	$109.10	$109.10
Purchase #7	$107.89	10.339%	$119.0447	$119.04	$119.05	$119.00
7 purchase totals =	$791.30		$848.9029	$848.89	$848.90	$849.00