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	$126.27	12.856%	$142.5033	$142.50	$142.50	$142.50
Purchase #2	$216.70	5.305%	$228.1959	$228.20	$228.20	$228.20
Purchase #3	$249.83	5.479%	$263.5182	$263.52	$263.50	$263.50
Purchase #4	$78.48	13.746%	$89.2679	$89.27	$89.25	$89.30
Purchase #5	$147.52	3.410%	$152.5504	$152.55	$152.55	$152.60
Purchase #6	$15.56	4.555%	$16.2688	$16.27	$16.25	$16.30
Purchase #7	$72.27	7.777%	$77.8904	$77.89	$77.90	$77.90
7 purchase totals =	$906.63		$970.1949	$970.20	$970.15	$970.30