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	$234.45	8.789%	$255.0558	$255.06	$255.05	$255.10
Purchase #2	$80.85	7.390%	$86.8248	$86.82	$86.80	$86.80
Purchase #3	$24.25	10.620%	$26.8254	$26.83	$26.85	$26.80
Purchase #4	$77.38	7.110%	$82.8817	$82.88	$82.90	$82.90
Purchase #5	$79.45	6.248%	$84.414	$84.41	$84.40	$84.40
Purchase #6	$76.51	6.578%	$81.5428	$81.54	$81.55	$81.50
Purchase #7	$150.64	5.454%	$158.8559	$158.86	$158.85	$158.90
7 purchase totals =	$723.53		$776.4004	$776.40	$776.40	$776.40