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	$238.97	4.227%	$249.0713	$249.07	$249.05	$249.10
Purchase #2	$111.39	4.679%	$116.6019	$116.60	$116.60	$116.60
Purchase #3	$221.68	6.407%	$235.883	$235.88	$235.90	$235.90
Purchase #4	$166.96	13.134%	$188.8885	$188.89	$188.90	$188.90
Purchase #5	$172.60	8.867%	$187.9044	$187.90	$187.90	$187.90
Purchase #6	$105.91	10.413%	$116.9384	$116.94	$116.95	$116.90
Purchase #7	$197.59	12.304%	$221.9015	$221.90	$221.90	$221.90
7 purchase totals =	$1,215.10		$1,317.1890	$1,317.18	$1,317.20	$1,317.20