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	$162.62	12.231%	$182.5101	$182.51	$182.50	$182.50
Purchase #2	$124.72	13.529%	$141.5934	$141.59	$141.60	$141.60
Purchase #3	$223.55	11.424%	$249.0884	$249.09	$249.10	$249.10
Purchase #4	$235.86	13.737%	$268.2601	$268.26	$268.25	$268.30
Purchase #5	$53.50	10.389%	$59.0581	$59.06	$59.05	$59.10
Purchase #6	$215.41	5.548%	$227.3609	$227.36	$227.35	$227.40
Purchase #7	$137.35	4.383%	$143.3701	$143.37	$143.35	$143.40
7 purchase totals =	$1,153.01		$1,271.2411	$1,271.24	$1,271.20	$1,271.40