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	$77.57	4.771%	$81.2709	$81.27	$81.25	$81.30
Purchase #2	$86.31	10.102%	$95.029	$95.03	$95.05	$95.00
Purchase #3	$120.83	10.427%	$133.4289	$133.43	$133.45	$133.40
Purchase #4	$47.94	13.167%	$54.2523	$54.25	$54.25	$54.30
Purchase #5	$60.72	6.250%	$64.515	$64.52	$64.50	$64.50
Purchase #6	$12.37	9.538%	$13.5499	$13.55	$13.55	$13.50
Purchase #7	$242.66	8.870%	$264.1839	$264.18	$264.20	$264.20
7 purchase totals =	$648.40		$706.2299	$706.23	$706.25	$706.20