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	$99.56	9.378%	$108.8967	$108.90	$108.90	$108.90
Purchase #2	$19.86	4.364%	$20.7267	$20.73	$20.75	$20.70
Purchase #3	$128.42	9.135%	$140.1512	$140.15	$140.15	$140.20
Purchase #4	$196.81	13.179%	$222.7476	$222.75	$222.75	$222.70
Purchase #5	$57.52	9.544%	$63.0097	$63.01	$63.00	$63.00
Purchase #6	$247.30	13.451%	$280.5643	$280.56	$280.55	$280.60
Purchase #7	$20.35	6.755%	$21.7246	$21.72	$21.70	$21.70
7 purchase totals =	$769.82		$857.8208	$857.82	$857.80	$857.80