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	$140.83	8.112%	$152.2541	$152.25	$152.25	$152.30
Purchase #2	$220.27	13.521%	$250.0527	$250.05	$250.05	$250.10
Purchase #3	$128.59	11.145%	$142.9214	$142.92	$142.90	$142.90
Purchase #4	$218.32	12.684%	$246.0117	$246.01	$246.00	$246.00
Purchase #5	$76.83	4.560%	$80.3334	$80.33	$80.35	$80.30
Purchase #6	$12.44	3.124%	$12.8286	$12.83	$12.85	$12.80
Purchase #7	$241.34	6.631%	$257.3433	$257.34	$257.35	$257.30
7 purchase totals =	$1,038.62		$1,141.7452	$1,141.73	$1,141.75	$1,141.70