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	$24.35	12.283%	$27.3409	$27.34	$27.35	$27.30
Purchase #2	$59.28	4.592%	$62.0021	$62.00	$62.00	$62.00
Purchase #3	$249.60	13.543%	$283.4033	$283.40	$283.40	$283.40
Purchase #4	$109.57	7.588%	$117.8842	$117.88	$117.90	$117.90
Purchase #5	$40.89	13.796%	$46.5312	$46.53	$46.55	$46.50
Purchase #6	$35.90	12.874%	$40.5218	$40.52	$40.50	$40.50
Purchase #7	$83.33	7.723%	$89.7656	$89.77	$89.75	$89.80
7 purchase totals =	$602.92		$667.4491	$667.44	$667.45	$667.40