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	$113.49	3.142%	$117.0559	$117.06	$117.05	$117.10
Purchase #2	$80.57	6.145%	$85.521	$85.52	$85.50	$85.50
Purchase #3	$16.29	3.336%	$16.8334	$16.83	$16.85	$16.80
Purchase #4	$27.50	6.705%	$29.3439	$29.34	$29.35	$29.30
Purchase #5	$185.74	7.798%	$200.224	$200.22	$200.20	$200.20
Purchase #6	$208.42	7.339%	$223.7159	$223.72	$223.70	$223.70
Purchase #7	$188.33	10.511%	$208.1254	$208.13	$208.15	$208.10
7 purchase totals =	$820.34		$880.8195	$880.82	$880.80	$880.70