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	$140.55	11.642%	$156.9128	$156.91	$156.90	$156.90
Purchase #2	$61.28	5.559%	$64.6866	$64.69	$64.70	$64.70
Purchase #3	$36.37	5.629%	$38.4173	$38.42	$38.40	$38.40
Purchase #4	$83.44	8.402%	$90.4506	$90.45	$90.45	$90.50
Purchase #5	$158.90	10.861%	$176.1581	$176.16	$176.15	$176.20
Purchase #6	$86.77	3.141%	$89.4954	$89.50	$89.50	$89.50
Purchase #7	$54.72	8.174%	$59.1928	$59.19	$59.20	$59.20
7 purchase totals =	$622.03		$675.3136	$675.32	$675.30	$675.40