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	$86.93	3.649%	$90.1021	$90.10	$90.10	$90.10
Purchase #2	$74.32	11.406%	$82.7969	$82.80	$82.80	$82.80
Purchase #3	$96.57	3.545%	$99.9934	$99.99	$100.00	$100.00
Purchase #4	$85.49	13.236%	$96.8055	$96.81	$96.80	$96.80
Purchase #5	$76.31	5.787%	$80.7261	$80.73	$80.75	$80.70
Purchase #6	$221.95	4.492%	$231.92	$231.92	$231.90	$231.90
Purchase #7	$122.68	12.645%	$138.1929	$138.19	$138.20	$138.20
7 purchase totals =	$764.25		$820.5369	$820.54	$820.55	$820.50