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	$53.43	7.744%	$57.5676	$57.57	$57.55	$57.60
Purchase #2	$68.26	12.828%	$77.0164	$77.02	$77.00	$77.00
Purchase #3	$56.54	3.665%	$58.6122	$58.61	$58.60	$58.60
Purchase #4	$54.61	9.117%	$59.5888	$59.59	$59.60	$59.60
Purchase #5	$28.95	11.456%	$32.2665	$32.27	$32.25	$32.30
Purchase #6	$144.35	12.506%	$162.4024	$162.40	$162.40	$162.40
Purchase #7	$237.66	8.552%	$257.9847	$257.98	$258.00	$258.00
7 purchase totals =	$643.80		$705.4386	$705.44	$705.40	$705.50