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	$143.49	5.578%	$151.4939	$151.49	$151.50	$151.50
Purchase #2	$168.50	5.732%	$178.1584	$178.16	$178.15	$178.20
Purchase #3	$103.71	11.870%	$116.0204	$116.02	$116.00	$116.00
Purchase #4	$39.60	11.483%	$44.1473	$44.15	$44.15	$44.10
Purchase #5	$72.80	13.359%	$82.5254	$82.53	$82.55	$82.50
Purchase #6	$225.45	6.644%	$240.4289	$240.43	$240.45	$240.40
Purchase #7	$182.88	13.730%	$207.9894	$207.99	$208.00	$208.00
7 purchase totals =	$936.43		$1,020.7637	$1,020.77	$1,020.80	$1,020.70