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	$37.77	3.743%	$39.1837	$39.18	$39.20	$39.20
Purchase #2	$154.48	6.615%	$164.6989	$164.70	$164.70	$164.70
Purchase #3	$51.56	7.191%	$55.2677	$55.27	$55.25	$55.30
Purchase #4	$29.43	10.811%	$32.6117	$32.61	$32.60	$32.60
Purchase #5	$72.87	11.861%	$81.5131	$81.51	$81.50	$81.50
Purchase #6	$105.79	5.502%	$111.6106	$111.61	$111.60	$111.60
Purchase #7	$240.80	12.170%	$270.1054	$270.11	$270.10	$270.10
7 purchase totals =	$692.70		$754.9911	$754.99	$754.95	$755.00