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	$227.72	9.286%	$248.8661	$248.87	$248.85	$248.90
Purchase #2	$245.48	4.664%	$256.9292	$256.93	$256.95	$256.90
Purchase #3	$59.83	3.408%	$61.869	$61.87	$61.85	$61.90
Purchase #4	$161.81	13.286%	$183.3081	$183.31	$183.30	$183.30
Purchase #5	$50.56	10.625%	$55.932	$55.93	$55.95	$55.90
Purchase #6	$69.44	13.116%	$78.5478	$78.55	$78.55	$78.50
Purchase #7	$101.70	10.199%	$112.0724	$112.07	$112.05	$112.10
7 purchase totals =	$916.54		$997.5246	$997.53	$997.50	$997.50