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	$50.56	11.750%	$56.5008	$56.50	$56.50	$56.50
Purchase #2	$52.91	3.142%	$54.5724	$54.57	$54.55	$54.60
Purchase #3	$98.60	11.393%	$109.8335	$109.83	$109.85	$109.80
Purchase #4	$178.98	3.582%	$185.3911	$185.39	$185.40	$185.40
Purchase #5	$31.88	6.669%	$34.0061	$34.01	$34.00	$34.00
Purchase #6	$72.94	12.715%	$82.2143	$82.21	$82.20	$82.20
Purchase #7	$134.62	8.567%	$146.1529	$146.15	$146.15	$146.20
7 purchase totals =	$620.49		$668.6711	$668.66	$668.65	$668.70