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	$34.80	3.151%	$35.8965	$35.90	$35.90	$35.90
Purchase #2	$33.26	12.400%	$37.3842	$37.38	$37.40	$37.40
Purchase #3	$185.30	3.687%	$192.132	$192.13	$192.15	$192.10
Purchase #4	$171.88	4.735%	$180.0185	$180.02	$180.00	$180.00
Purchase #5	$211.63	12.522%	$238.1303	$238.13	$238.15	$238.10
Purchase #6	$90.51	11.866%	$101.2499	$101.25	$101.25	$101.20
Purchase #7	$100.64	7.828%	$108.5181	$108.52	$108.50	$108.50
7 purchase totals =	$828.02		$893.3295	$893.33	$893.35	$893.20