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	$55.60	6.555%	$59.2446	$59.24	$59.25	$59.20
Purchase #2	$237.30	10.337%	$261.8297	$261.83	$261.85	$261.80
Purchase #3	$111.54	4.633%	$116.7076	$116.71	$116.70	$116.70
Purchase #4	$164.92	10.842%	$182.8006	$182.80	$182.80	$182.80
Purchase #5	$23.89	6.772%	$25.5078	$25.51	$25.50	$25.50
Purchase #6	$73.60	13.507%	$83.5412	$83.54	$83.55	$83.50
Purchase #7	$44.91	12.379%	$50.4694	$50.47	$50.45	$50.50
7 purchase totals =	$711.76		$780.1009	$780.10	$780.10	$780.00