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	$128.82	9.870%	$141.5345	$141.53	$141.55	$141.50
Purchase #2	$129.86	5.640%	$137.1841	$137.18	$137.20	$137.20
Purchase #3	$80.54	10.424%	$88.9355	$88.94	$88.95	$88.90
Purchase #4	$63.70	5.238%	$67.0366	$67.04	$67.05	$67.00
Purchase #5	$83.47	7.556%	$89.777	$89.78	$89.80	$89.80
Purchase #6	$8.80	3.304%	$9.0908	$9.09	$9.10	$9.10
Purchase #7	$118.59	3.624%	$122.8877	$122.89	$122.90	$122.90
7 purchase totals =	$613.78		$656.4462	$656.45	$656.55	$656.40