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	$157.60	4.111%	$164.0789	$164.08	$164.10	$164.10
Purchase #2	$153.72	12.210%	$172.4892	$172.49	$172.50	$172.50
Purchase #3	$245.89	6.280%	$261.3319	$261.33	$261.35	$261.30
Purchase #4	$6.61	8.619%	$7.1797	$7.18	$7.20	$7.20
Purchase #5	$105.26	3.554%	$109.0009	$109.00	$109.00	$109.00
Purchase #6	$102.29	12.108%	$114.6753	$114.68	$114.70	$114.70
Purchase #7	$37.79	7.774%	$40.7278	$40.73	$40.75	$40.70
7 purchase totals =	$809.16		$869.4837	$869.49	$869.60	$869.50