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	$233.43	11.114%	$259.3734	$259.37	$259.35	$259.40
Purchase #2	$175.56	8.444%	$190.3843	$190.38	$190.40	$190.40
Purchase #3	$160.93	9.818%	$176.7301	$176.73	$176.75	$176.70
Purchase #4	$246.72	13.718%	$280.565	$280.57	$280.55	$280.60
Purchase #5	$129.85	9.863%	$142.6571	$142.66	$142.65	$142.70
Purchase #6	$36.63	3.466%	$37.8996	$37.90	$37.90	$37.90
Purchase #7	$79.83	12.198%	$89.5677	$89.57	$89.55	$89.60
7 purchase totals =	$1,062.95		$1,177.1772	$1,177.18	$1,177.15	$1,177.30