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	$209.79	13.275%	$237.6396	$237.64	$237.65	$237.60
Purchase #2	$240.70	11.276%	$267.8413	$267.84	$267.85	$267.80
Purchase #3	$71.58	10.569%	$79.1453	$79.15	$79.15	$79.10
Purchase #4	$47.93	5.429%	$50.5321	$50.53	$50.55	$50.50
Purchase #5	$89.64	12.126%	$100.5097	$100.51	$100.50	$100.50
Purchase #6	$168.59	11.270%	$187.5901	$187.59	$187.60	$187.60
Purchase #7	$247.38	13.438%	$280.6229	$280.62	$280.60	$280.60
7 purchase totals =	$1,075.61		$1,203.8810	$1,203.88	$1,203.90	$1,203.70