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	$12.33	4.810%	$12.9231	$12.92	$12.90	$12.90
Purchase #2	$203.32	8.152%	$219.8946	$219.89	$219.90	$219.90
Purchase #3	$54.68	12.544%	$61.5391	$61.54	$61.55	$61.50
Purchase #4	$58.25	13.300%	$65.9973	$66.00	$66.00	$66.00
Purchase #5	$158.76	7.722%	$171.0194	$171.02	$171.00	$171.00
Purchase #6	$96.90	4.830%	$101.5803	$101.58	$101.60	$101.60
Purchase #7	$90.93	11.495%	$101.3824	$101.38	$101.40	$101.40
7 purchase totals =	$675.17		$734.3362	$734.33	$734.35	$734.30