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	$75.50	8.604%	$81.996	$82.00	$82.00	$82.00
Purchase #2	$78.30	13.649%	$88.9872	$88.99	$89.00	$89.00
Purchase #3	$164.42	4.321%	$171.5246	$171.52	$171.50	$171.50
Purchase #4	$170.57	6.866%	$182.2813	$182.28	$182.30	$182.30
Purchase #5	$16.31	11.358%	$18.1625	$18.16	$18.15	$18.20
Purchase #6	$168.71	13.343%	$191.221	$191.22	$191.20	$191.20
Purchase #7	$82.98	11.419%	$92.4555	$92.46	$92.45	$92.50
7 purchase totals =	$756.79		$826.6281	$826.63	$826.60	$826.70