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	$167.84	10.737%	$185.861	$185.86	$185.85	$185.90
Purchase #2	$166.55	12.682%	$187.6719	$187.67	$187.65	$187.70
Purchase #3	$242.79	11.746%	$271.3081	$271.31	$271.30	$271.30
Purchase #4	$127.95	3.580%	$132.5306	$132.53	$132.55	$132.50
Purchase #5	$19.80	7.196%	$21.2248	$21.22	$21.20	$21.20
Purchase #6	$88.64	7.441%	$95.2357	$95.24	$95.25	$95.20
Purchase #7	$129.31	11.732%	$144.4806	$144.48	$144.50	$144.50
7 purchase totals =	$942.88		$1,038.3127	$1,038.31	$1,038.30	$1,038.30