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	$170.86	6.800%	$182.4785	$182.48	$182.50	$182.50
Purchase #2	$168.39	13.598%	$191.2877	$191.29	$191.30	$191.30
Purchase #3	$10.32	11.239%	$11.4799	$11.48	$11.50	$11.50
Purchase #4	$24.98	8.473%	$27.0966	$27.10	$27.10	$27.10
Purchase #5	$68.85	4.782%	$72.1424	$72.14	$72.15	$72.10
Purchase #6	$136.71	13.251%	$154.8254	$154.83	$154.85	$154.80
Purchase #7	$184.27	11.122%	$204.7645	$204.76	$204.75	$204.80
7 purchase totals =	$764.38		$844.0750	$844.08	$844.15	$844.10