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	$168.55	9.864%	$185.1758	$185.18	$185.20	$185.20
Purchase #2	$111.95	8.821%	$121.8251	$121.83	$121.85	$121.80
Purchase #3	$92.43	12.722%	$104.1889	$104.19	$104.20	$104.20
Purchase #4	$46.32	9.726%	$50.8251	$50.83	$50.85	$50.80
Purchase #5	$247.42	12.547%	$278.4638	$278.46	$278.45	$278.50
Purchase #6	$75.59	9.730%	$82.9449	$82.94	$82.95	$82.90
Purchase #7	$90.47	6.179%	$96.0601	$96.06	$96.05	$96.10
7 purchase totals =	$832.73		$919.4837	$919.49	$919.55	$919.50