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	$179.76	3.696%	$186.4039	$186.40	$186.40	$186.40
Purchase #2	$247.45	13.328%	$280.4301	$280.43	$280.45	$280.40
Purchase #3	$99.29	5.553%	$104.8036	$104.80	$104.80	$104.80
Purchase #4	$107.34	7.733%	$115.6406	$115.64	$115.65	$115.60
Purchase #5	$9.50	11.275%	$10.5711	$10.57	$10.55	$10.60
Purchase #6	$84.82	5.574%	$89.5479	$89.55	$89.55	$89.50
Purchase #7	$167.70	12.337%	$188.3891	$188.39	$188.40	$188.40
7 purchase totals =	$895.86		$975.7863	$975.78	$975.80	$975.70