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	$131.82	4.786%	$138.1289	$138.13	$138.15	$138.10
Purchase #2	$163.57	13.671%	$185.9317	$185.93	$185.95	$185.90
Purchase #3	$101.96	4.268%	$106.3117	$106.31	$106.30	$106.30
Purchase #4	$248.74	13.526%	$282.3846	$282.38	$282.40	$282.40
Purchase #5	$91.41	13.491%	$103.7421	$103.74	$103.75	$103.70
Purchase #6	$108.71	13.284%	$123.151	$123.15	$123.15	$123.20
Purchase #7	$12.97	4.292%	$13.5267	$13.53	$13.55	$13.50
7 purchase totals =	$859.18		$953.1767	$953.17	$953.25	$953.10