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	$33.72	12.156%	$37.819	$37.82	$37.80	$37.80
Purchase #2	$51.81	10.304%	$57.1485	$57.15	$57.15	$57.10
Purchase #3	$205.50	8.644%	$223.2634	$223.26	$223.25	$223.30
Purchase #4	$168.79	3.300%	$174.3601	$174.36	$174.35	$174.40
Purchase #5	$178.62	7.699%	$192.372	$192.37	$192.35	$192.40
Purchase #6	$95.99	7.697%	$103.3784	$103.38	$103.40	$103.40
Purchase #7	$134.35	5.396%	$141.5995	$141.60	$141.60	$141.60
7 purchase totals =	$868.78		$929.9409	$929.94	$929.90	$930.00