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	$72.76	6.189%	$77.2631	$77.26	$77.25	$77.30
Purchase #2	$54.52	13.520%	$61.8911	$61.89	$61.90	$61.90
Purchase #3	$96.44	6.260%	$102.4771	$102.48	$102.50	$102.50
Purchase #4	$52.94	12.524%	$59.5702	$59.57	$59.55	$59.60
Purchase #5	$163.25	8.118%	$176.5026	$176.50	$176.50	$176.50
Purchase #6	$246.41	3.312%	$254.5711	$254.57	$254.55	$254.60
Purchase #7	$238.74	8.321%	$258.6056	$258.61	$258.60	$258.60
7 purchase totals =	$925.06		$990.8808	$990.88	$990.85	$991.00