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	$80.83	5.638%	$85.3872	$85.39	$85.40	$85.40
Purchase #2	$39.78	6.118%	$42.2137	$42.21	$42.20	$42.20
Purchase #3	$32.82	8.437%	$35.589	$35.59	$35.60	$35.60
Purchase #4	$110.78	8.789%	$120.5165	$120.52	$120.50	$120.50
Purchase #5	$157.82	9.506%	$172.8224	$172.82	$172.80	$172.80
Purchase #6	$37.29	5.701%	$39.4159	$39.42	$39.40	$39.40
Purchase #7	$34.99	9.175%	$38.2003	$38.20	$38.20	$38.20
7 purchase totals =	$494.31		$534.1450	$534.15	$534.10	$534.10