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	$95.78	11.493%	$106.788	$106.79	$106.80	$106.80
Purchase #2	$185.58	3.669%	$192.3889	$192.39	$192.40	$192.40
Purchase #3	$45.30	8.304%	$49.0617	$49.06	$49.05	$49.10
Purchase #4	$166.78	4.110%	$173.6347	$173.63	$173.65	$173.60
Purchase #5	$40.96	6.682%	$43.6969	$43.70	$43.70	$43.70
Purchase #6	$104.92	4.755%	$109.9089	$109.91	$109.90	$109.90
Purchase #7	$136.32	4.795%	$142.8565	$142.86	$142.85	$142.90
7 purchase totals =	$775.64		$818.3356	$818.34	$818.35	$818.40