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	$241.73	3.191%	$249.4436	$249.44	$249.45	$249.40
Purchase #2	$139.67	11.203%	$155.3172	$155.32	$155.30	$155.30
Purchase #3	$245.97	6.269%	$261.3899	$261.39	$261.40	$261.40
Purchase #4	$13.37	11.440%	$14.8995	$14.90	$14.90	$14.90
Purchase #5	$117.31	11.631%	$130.9543	$130.95	$130.95	$131.00
Purchase #6	$142.31	4.148%	$148.213	$148.21	$148.20	$148.20
Purchase #7	$172.59	10.128%	$190.0699	$190.07	$190.05	$190.10
7 purchase totals =	$1,072.95		$1,150.2874	$1,150.28	$1,150.25	$1,150.30