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	$35.95	8.288%	$38.9295	$38.93	$38.95	$38.90
Purchase #2	$153.79	11.328%	$171.2113	$171.21	$171.20	$171.20
Purchase #3	$218.72	3.381%	$226.1149	$226.11	$226.10	$226.10
Purchase #4	$136.89	3.163%	$141.2198	$141.22	$141.20	$141.20
Purchase #5	$106.96	4.207%	$111.4598	$111.46	$111.45	$111.50
Purchase #6	$47.87	12.673%	$53.9366	$53.94	$53.95	$53.90
Purchase #7	$78.93	12.409%	$88.7244	$88.72	$88.70	$88.70
7 purchase totals =	$779.11		$831.5963	$831.59	$831.55	$831.50