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	$52.29	12.636%	$58.8974	$58.90	$58.90	$58.90
Purchase #2	$247.48	4.187%	$257.842	$257.84	$257.85	$257.80
Purchase #3	$29.86	4.647%	$31.2476	$31.25	$31.25	$31.20
Purchase #4	$177.85	4.127%	$185.1899	$185.19	$185.20	$185.20
Purchase #5	$158.29	13.437%	$179.5594	$179.56	$179.55	$179.60
Purchase #6	$193.99	12.666%	$218.5608	$218.56	$218.55	$218.60
Purchase #7	$75.99	12.234%	$85.2866	$85.29	$85.30	$85.30
7 purchase totals =	$935.75		$1,016.5837	$1,016.59	$1,016.60	$1,016.60