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	$28.52	9.824%	$31.3218	$31.32	$31.30	$31.30
Purchase #2	$83.28	6.276%	$88.5067	$88.51	$88.50	$88.50
Purchase #3	$169.48	12.480%	$190.6311	$190.63	$190.65	$190.60
Purchase #4	$96.63	3.691%	$100.1966	$100.20	$100.20	$100.20
Purchase #5	$124.25	13.825%	$141.4276	$141.43	$141.45	$141.40
Purchase #6	$68.88	13.559%	$78.2194	$78.22	$78.20	$78.20
Purchase #7	$65.34	12.215%	$73.3213	$73.32	$73.30	$73.30
7 purchase totals =	$636.38		$703.6245	$703.63	$703.60	$703.50