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	$246.90	12.604%	$278.0193	$278.02	$278.00	$278.00
Purchase #2	$207.34	4.113%	$215.8679	$215.87	$215.85	$215.90
Purchase #3	$116.82	12.557%	$131.4891	$131.49	$131.50	$131.50
Purchase #4	$73.38	7.188%	$78.6546	$78.65	$78.65	$78.70
Purchase #5	$71.47	12.307%	$80.2658	$80.27	$80.25	$80.30
Purchase #6	$64.78	9.282%	$70.7929	$70.79	$70.80	$70.80
Purchase #7	$175.51	9.709%	$192.5503	$192.55	$192.55	$192.60
7 purchase totals =	$956.20		$1,047.6399	$1,047.64	$1,047.60	$1,047.80