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	$18.63	7.844%	$20.0913	$20.09	$20.10	$20.10
Purchase #2	$211.85	4.521%	$221.4277	$221.43	$221.45	$221.40
Purchase #3	$33.32	12.180%	$37.3784	$37.38	$37.40	$37.40
Purchase #4	$226.58	5.410%	$238.838	$238.84	$238.85	$238.80
Purchase #5	$235.75	11.827%	$263.6322	$263.63	$263.65	$263.60
Purchase #6	$221.96	7.359%	$238.294	$238.29	$238.30	$238.30
Purchase #7	$19.88	3.537%	$20.5832	$20.58	$20.60	$20.60
7 purchase totals =	$967.97		$1,040.2448	$1,040.24	$1,040.35	$1,040.20