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	$166.92	11.386%	$185.9255	$185.93	$185.95	$185.90
Purchase #2	$95.87	12.699%	$108.0445	$108.04	$108.05	$108.00
Purchase #3	$18.97	6.871%	$20.2734	$20.27	$20.25	$20.30
Purchase #4	$137.53	5.523%	$145.1258	$145.13	$145.15	$145.10
Purchase #5	$167.32	9.235%	$182.772	$182.77	$182.75	$182.80
Purchase #6	$86.42	3.377%	$89.3384	$89.34	$89.35	$89.30
Purchase #7	$174.81	8.402%	$189.4975	$189.50	$189.50	$189.50
7 purchase totals =	$847.84		$920.9771	$920.98	$921.00	$920.90