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	$249.29	12.648%	$280.8202	$280.82	$280.80	$280.80
Purchase #2	$73.69	11.703%	$82.3139	$82.31	$82.30	$82.30
Purchase #3	$60.31	3.772%	$62.5849	$62.58	$62.60	$62.60
Purchase #4	$211.59	6.396%	$225.1233	$225.12	$225.10	$225.10
Purchase #5	$195.86	4.789%	$205.2397	$205.24	$205.25	$205.20
Purchase #6	$113.47	4.456%	$118.5262	$118.53	$118.55	$118.50
Purchase #7	$89.35	11.708%	$99.8111	$99.81	$99.80	$99.80
7 purchase totals =	$993.56		$1,074.4193	$1,074.41	$1,074.40	$1,074.30