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	$59.63	6.558%	$63.5405	$63.54	$63.55	$63.50
Purchase #2	$133.86	4.653%	$140.0885	$140.09	$140.10	$140.10
Purchase #3	$236.48	3.540%	$244.8514	$244.85	$244.85	$244.90
Purchase #4	$53.72	8.579%	$58.3286	$58.33	$58.35	$58.30
Purchase #5	$164.90	13.389%	$186.9785	$186.98	$187.00	$187.00
Purchase #6	$106.98	3.778%	$111.0217	$111.02	$111.00	$111.00
Purchase #7	$40.87	6.340%	$43.4612	$43.46	$43.45	$43.50
7 purchase totals =	$796.44		$848.2704	$848.27	$848.30	$848.30