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	$35.58	9.219%	$38.8601	$38.86	$38.85	$38.90
Purchase #2	$141.37	7.721%	$152.2852	$152.29	$152.30	$152.30
Purchase #3	$113.95	8.421%	$123.5457	$123.55	$123.55	$123.50
Purchase #4	$110.82	7.272%	$118.8788	$118.88	$118.90	$118.90
Purchase #5	$164.62	12.824%	$185.7309	$185.73	$185.75	$185.70
Purchase #6	$198.41	9.679%	$217.6141	$217.61	$217.60	$217.60
Purchase #7	$77.86	5.269%	$81.9624	$81.96	$81.95	$82.00
7 purchase totals =	$842.61		$918.8772	$918.88	$918.90	$918.90