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	$231.80	12.556%	$260.9048	$260.90	$260.90	$260.90
Purchase #2	$47.78	9.804%	$52.4644	$52.46	$52.45	$52.50
Purchase #3	$10.86	5.825%	$11.4926	$11.49	$11.50	$11.50
Purchase #4	$233.55	4.121%	$243.1746	$243.17	$243.15	$243.20
Purchase #5	$212.96	9.441%	$233.0656	$233.07	$233.05	$233.10
Purchase #6	$196.25	13.849%	$223.4287	$223.43	$223.45	$223.40
Purchase #7	$247.25	13.559%	$280.7746	$280.77	$280.75	$280.80
7 purchase totals =	$1,180.45		$1,305.3053	$1,305.29	$1,305.25	$1,305.40