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	$38.39	4.601%	$40.1563	$40.16	$40.15	$40.20
Purchase #2	$53.79	10.378%	$59.3723	$59.37	$59.35	$59.40
Purchase #3	$170.28	9.151%	$185.8623	$185.86	$185.85	$185.90
Purchase #4	$85.86	4.277%	$89.5322	$89.53	$89.55	$89.50
Purchase #5	$117.34	3.209%	$121.1054	$121.11	$121.10	$121.10
Purchase #6	$18.67	3.266%	$19.2798	$19.28	$19.30	$19.30
Purchase #7	$207.85	3.842%	$215.8356	$215.84	$215.85	$215.80
7 purchase totals =	$692.18		$731.1439	$731.15	$731.15	$731.20