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	$119.63	9.554%	$131.0595	$131.06	$131.05	$131.10
Purchase #2	$42.63	8.728%	$46.3507	$46.35	$46.35	$46.40
Purchase #3	$79.53	4.288%	$82.9402	$82.94	$82.95	$82.90
Purchase #4	$28.65	13.287%	$32.4567	$32.46	$32.45	$32.50
Purchase #5	$157.26	4.508%	$164.3493	$164.35	$164.35	$164.30
Purchase #6	$149.72	7.140%	$160.41	$160.41	$160.40	$160.40
Purchase #7	$247.86	13.329%	$280.8973	$280.90	$280.90	$280.90
7 purchase totals =	$825.28		$898.4637	$898.47	$898.45	$898.50