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	$247.27	3.764%	$256.5772	$256.58	$256.60	$256.60
Purchase #2	$53.96	6.457%	$57.4442	$57.44	$57.45	$57.40
Purchase #3	$61.81	11.258%	$68.7686	$68.77	$68.75	$68.80
Purchase #4	$46.48	9.796%	$51.0332	$51.03	$51.05	$51.00
Purchase #5	$24.93	13.471%	$28.2883	$28.29	$28.30	$28.30
Purchase #6	$187.80	4.863%	$196.9327	$196.93	$196.95	$196.90
Purchase #7	$133.48	5.843%	$141.2792	$141.28	$141.30	$141.30
7 purchase totals =	$755.73		$800.3234	$800.32	$800.40	$800.30