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	$17.79	3.403%	$18.3954	$18.40	$18.40	$18.40
Purchase #2	$96.67	4.800%	$101.3102	$101.31	$101.30	$101.30
Purchase #3	$139.96	7.416%	$150.3394	$150.34	$150.35	$150.30
Purchase #4	$153.35	4.242%	$159.8551	$159.86	$159.85	$159.90
Purchase #5	$39.89	13.622%	$45.3238	$45.32	$45.30	$45.30
Purchase #6	$166.96	12.537%	$187.8918	$187.89	$187.90	$187.90
Purchase #7	$78.96	12.103%	$88.5165	$88.52	$88.50	$88.50
7 purchase totals =	$693.58		$751.6322	$751.64	$751.60	$751.60